Merge pull request #174 from ipnet-mesh/feature/improve-snr-path-visibility

Add observer detail rows with SNR/path data and UI polish
2026-08-09 02:12:53 +02:00 · 2026-04-26 13:05:10 +01:00
parent a0d59748f2 e867f0074a
commit e4655a6b59
30 changed files with 1208 additions and 203 deletions
@@ -189,6 +189,11 @@ Group/broadcast messages on specific channels.
 - Payload type `4` location metadata (`appData.location.latitude/longitude`) is mapped to node `lat/lon` for map rendering.
 - This keeps advertisement persistence aligned with meshcore-packet-capture expectations (advertisement traffic only).

+**Compatibility ingest note (envelope fields)**:
+- The LetsMesh upload envelope carries `SNR` and `path` fields alongside the decoded packet payload. These are available on all packet types (messages, advertisements, traces, telemetry).
+- The normalizer extracts `SNR` (normalized to lowercase `snr`) and `path` (converted to `path_len` via hop count) from the envelope and includes them in the normalized payload.
+- Per-observer `snr` and `path_len` are stored in the `event_observers` junction table, allowing each observer to record its own signal strength and hop count.
+
 **Compatibility ingest note (non-message structured events)**:
 - Decoded payload type `9` is normalized to `TRACE_DATA` (`traceTag`, flags, auth, path hashes, and SNR values).
 - Decoded payload type `11` (`Control/NodeDiscoverResp`) is normalized to `contact` events for node upsert parity.
@@ -514,6 +519,22 @@ See [AGENTS.md](AGENTS.md) for webhook configuration details.

 ---

+## API Response: Observer Info
+
+Events that support multi-observer tracking (messages, advertisements, trace paths, telemetry) include an `observers` array in API responses. Each observer entry contains:
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `node_id` | string (UUID) | Observer node UUID |
+| `public_key` | string (64 hex chars) | Observer node public key |
+| `name` | string or null | Observer node advertised name |
+| `tag_name` | string or null | Observer name from node tags |
+| `snr` | number or null | Signal-to-noise ratio at this observer (dB) |
+| `path_len` | integer or null | Hop count at this observer |
+| `observed_at` | string (ISO 8601) | When this observer captured the event |
+
+---
+
 ## Event Flow

 1. **Hardware/Mock MeshCore** → Generates raw events
@@ -0,0 +1,45 @@
+"""add path_len to event_observers
+
+Revision ID: a10dbca883a2
+Revises: b1c2d3e4f5a6
+Create Date: 2026-04-26 10:52:09.664958+00:00
+
+"""
+
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision: str = "a10dbca883a2"
+down_revision: Union[str, None] = "b1c2d3e4f5a6"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    with op.batch_alter_table("event_observers", schema=None) as batch_op:
+        batch_op.add_column(sa.Column("path_len", sa.Integer(), nullable=True))
+        batch_op.drop_constraint(
+            batch_op.f("uq_event_receivers_hash_node"), type_="unique"
+        )
+        batch_op.create_unique_constraint(
+            "uq_event_observers_hash_node", ["event_hash", "observer_node_id"]
+        )
+
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    with op.batch_alter_table("event_observers", schema=None) as batch_op:
+        batch_op.drop_constraint("uq_event_observers_hash_node", type_="unique")
+        batch_op.create_unique_constraint(
+            batch_op.f("uq_event_receivers_hash_node"),
+            ["event_hash", "observer_node_id"],
+        )
+        batch_op.drop_column("path_len")
+
+    # ### end Alembic commands ###
@@ -0,0 +1,342 @@
+# Observer Detail Rows — Implementation Plan
+
+**Date:** 2026-04-26
+**Status:** Approved
+
+## Decisions
+
+1. **No backfill** — Historical data unchanged. Per-observer `path_len` only captured for new events.
+2. **Canonical case: lowercase `snr`** — All code normalizes SNR references to lowercase.
+3. **Trace observer pattern** — Per-observer `path_len` tracks the observer's hop count to the event source.
+
+## Terminology
+
+The original research used outdated names. This plan uses the correct codebase terminology:
+
+| Old Reference | Actual Codebase |
+|---------------|-----------------|
+| `event_receivers` | `event_observers` |
+| `add_event_receiver()` | `add_event_observer()` |
+| `_fetch_receivers_for_events()` | `_fetch_observers_for_events()` |
+| `ReceiverInfo` | `ObserverInfo` |
+| `receivers` (API field) | `observers` |
+
+## Verified Current State
+
+### Database (`event_observers` table)
+
+```
+event_observers
+├── id                UUID PK
+├── event_type        String(20)
+├── event_hash        String(32)
+├── observer_node_id  FK → nodes.id
+├── snr               Float (nullable)
+├── observed_at       DateTime
+├── created_at        DateTime
+└── updated_at        DateTime
+```
+
+**Missing:** `path_len` column.
+
+### Per-Event vs Per-Observer Fields
+
+| Field | Scope | Rationale |
+|-------|-------|-----------|
+| `snr` | **Per-observer** | Signal strength differs by observer location |
+| `path_len` | **Per-observer** | Hop count differs by observer position in mesh topology |
+| `observed_at` | **Per-observer** | Each observer sees the event at a different time |
+| `snr_values` (trace) | **Per-event only** | Per-hop SNR along the trace path |
+| `hop_count` (trace) | **Per-event only** | Total hops in the trace |
+
+### Handler Payload Extraction
+
+| Handler | SNR extraction | path_len extraction |
+|---------|---------------|-------------------|
+| `message.py` | `payload.get("SNR") or payload.get("snr")` | `payload.get("path_len")` |
+| `advertisement.py` | None | None |
+| `trace.py` | None | `payload.get("path_len")` |
+| `telemetry.py` | None | None |
+
+Each handler has exactly 3 `add_event_observer()` call sites:
+1. Duplicate path (existing event)
+2. First observer (new event)
+3. Race condition recovery
+
+All call sites need `path_len` parameter.
+
+### LetsMesh Normalizer
+
+`_build_letsmesh_advertisement_payload()` (handles decoded packet type 4) does NOT extract envelope `SNR` or `path`. The message payload method already does (lines 143-160). **Note:** The message method outputs `normalized_payload["SNR"]` (uppercase) at line 160, which contradicts Decision #2. This must be changed to lowercase `"snr"` alongside the advertisement fix.
+
+### API Routes
+
+| Route | Populates `observers`? | Notes |
+|-------|----------------------|-------|
+| `api/routes/messages.py` | Yes | Uses `_fetch_observers_for_events()` |
+| `api/routes/advertisements.py` | Yes | Uses `_fetch_observers_for_events()` |
+| `api/routes/trace_paths.py` | No — returns `[]` | Schema has field but never queries |
+| `api/routes/telemetry.py` | No — returns `[]` | Same issue |
+
+`_fetch_observers_for_events()` is duplicated identically in `messages.py` and `advertisements.py`.
+
+### Frontend
+
+- **`components.js:444` `receiverIcons()`** — Dead code. Uses wrong property names (`receiver_node_name` / `receiver_node_public_key`). No page imports it.
+- **`messages.js` and `advertisements.js`** — Render satellite dish icons with correct property names (`recv.tag_name`, `recv.name`, `recv.public_key`) but display name-only tooltips. Per-observer SNR/path_len is returned by API but never displayed.
+- **No trace_paths.js or telemetry.js frontend pages exist.**
+- **No expandable/collapsible row patterns** exist anywhere in the SPA.
+
+### Schema (`ObserverInfo`)
+
+```python
+class ObserverInfo(BaseModel):
+    node_id: str
+    public_key: str
+    name: Optional[str]
+    tag_name: Optional[str]
+    snr: Optional[float]
+    observed_at: datetime
+```
+
+**Missing:** `path_len` field.
+
+---
+
+## Implementation Plan
+
+### Phase 1: Database Schema — Add `path_len` to `event_observers`
+
+**File:** `src/meshcore_hub/common/models/event_observer.py`
+
+- Add column: `path_len: Mapped[Optional[int]] = mapped_column(Integer, nullable=True)`
+- Update `add_event_observer()` signature to accept `path_len: Optional[int] = None`
+- Include `path_len` in `sqlite_insert().values()` call
+
+**Migration:**
+```bash
+source .venv/bin/activate
+meshcore-hub db revision --autogenerate -m "add path_len to event_observers"
+meshcore-hub db upgrade
+```
+
+### Phase 2: API Utility & Schema
+
+**New file:** `src/meshcore_hub/api/observer_utils.py`
+
+Move `_fetch_observers_for_events()` into a shared module. Update the query to also select `EventObserver.path_len`.
+
+```python
+def _fetch_observers_for_events(
+    session: DbSession,
+    event_type: str,
+    event_hashes: list[str],
+) -> dict[str, list[ObserverInfo]]:
+```
+
+The query selects: `EventObserver.event_hash`, `EventObserver.snr`, `EventObserver.path_len`, `EventObserver.observed_at`, `Node.id`, `Node.public_key`, `Node.name`. Also fetches `NodeTag` name tags.
+
+**Schema update:** `src/meshcore_hub/common/schemas/messages.py`
+
+Add to `ObserverInfo`:
+```python
+path_len: Optional[int] = Field(default=None, description="Hop count at this observer")
+```
+
+**Route updates:**
+
+| File | Change |
+|------|--------|
+| `api/routes/messages.py` | Remove local `_fetch_observers_for_events`, import from `observer_utils` |
+| `api/routes/advertisements.py` | Same |
+| `api/routes/trace_paths.py` | Import and call `_fetch_observers_for_events(session, "trace", event_hashes)` to populate `observers` |
+| `api/routes/telemetry.py` | Import and call `_fetch_observers_for_events(session, "telemetry", event_hashes)` to populate `observers` |
+
+### Phase 3: LetsMesh Normalizer — Extract Envelope SNR & Path for Advertisements
+
+**File:** `src/meshcore_hub/collector/letsmesh_normalizer.py`
+
+In `_build_letsmesh_advertisement_payload()`, add after the `normalized_payload` dict initialization (line 574):
+
+```python
+snr = self._parse_float(payload.get("SNR"))
+if snr is None:
+    snr = self._parse_float(payload.get("snr"))
+if snr is not None:
+    normalized_payload["snr"] = snr
+
+path_len = self._parse_path_length(payload.get("path"))
+if path_len is not None:
+    normalized_payload["path_len"] = path_len
+```
+
+This follows the same pattern used in `_build_letsmesh_message_payload()` (lines 143-160), with the key difference being lowercase `"snr"` output.
+
+> **Inaccuracy corrected (review 2026-04-26):** The message normalizer at line 160 outputs `normalized_payload["SNR"]` (uppercase). Phase 4 below removes the handler's uppercase fallback (`payload.get("SNR") or ...`). Without also fixing the normalizer output, LetsMesh-routed messages would lose SNR data. The change below is added to enforce Decision #2 (canonical lowercase `snr`) consistently.
+
+In `_build_letsmesh_message_payload()`, change line 160:
+```python
+# Before:
+normalized_payload["SNR"] = snr
+# After:
+normalized_payload["snr"] = snr
+```
+
+### Phase 4: Collector Handlers — Pass SNR & path_len
+
+**File:** `src/meshcore_hub/collector/handlers/message.py`
+
+- Change line 78: `payload.get("SNR") or payload.get("snr")` → `payload.get("snr")`
+- `path_len` is already extracted (line 75) — just pass it to all 3 `add_event_observer()` call sites (lines 124, 158, 178)
+
+**File:** `src/meshcore_hub/collector/handlers/advertisement.py`
+
+- Add extraction: `snr = payload.get("snr")`
+- Add extraction: `path_len = payload.get("path_len")`
+- Pass both to all 3 `add_event_observer()` call sites (lines 120, 182, 203)
+
+**File:** `src/meshcore_hub/collector/handlers/trace.py`
+
+- Add extraction: `snr = payload.get("snr")`
+- `path_len` is already extracted (line 38) — pass both to all 3 `add_event_observer()` call sites (lines 74, 106, 126)
+
+**File:** `src/meshcore_hub/collector/handlers/telemetry.py`
+
+- Add extraction: `snr = payload.get("snr")`
+- Add extraction: `path_len = payload.get("path_len")`
+- Pass both to all 3 `add_event_observer()` call sites (lines 87, 133, 154)
+
+### Phase 5: Frontend Components
+
+**File:** `src/meshcore_hub/web/static/js/spa/components.js`
+
+- **Remove** dead `receiverIcons()` function (lines 444-452) — uses wrong property names, no page imports it
+- **Add** `observerDetailRow(observers, eventProperties)` component:
+  - Renders an expandable sub-table below the event row
+  - Observer columns:
+    - **Observer** — `tag_name || name || truncateKey(public_key, 12)`, linked to `/nodes/${public_key}`
+    - **SNR** — Formatted as "X.X dB" or "—" if null
+    - **Path** — Formatted as "N hops" or "—" if null
+    - **Received** — Relative time via `formatRelativeTime(observed_at)`
+  - `eventProperties` parameter for event-level context (e.g., trace `snr_values`)
+  - Toggle helper: click event row to show/hide `.observer-detail` row below it
+- **Add** `observerIcons(observers)` — count badge with tooltip listing observer names
+
+**File:** `src/meshcore_hub/web/static/css/app.css`
+
+- `.observer-detail` expandable row styles (indented, compact sub-table)
+- CSS transition for smooth expand/collapse (max-height animation)
+- Responsive: desktop table vs mobile card layout
+
+### Phase 6: Frontend Pages
+
+**File:** `src/meshcore_hub/web/static/js/spa/pages/messages.js`
+
+Replace current satellite dish icon rendering with:
+- Observer count badge in the Receivers column (clickable to expand)
+- Expandable detail row showing per-observer: name, SNR, path_len, observed_at
+- Both desktop table (~line 255) and mobile card (~line 206) views
+
+**File:** `src/meshcore_hub/web/static/js/spa/pages/advertisements.js`
+
+Same pattern as messages.
+- Desktop table (~line 135)
+- Mobile card (~line 99)
+
+**Note:** No `trace_paths.js` frontend page exists. No frontend changes needed for trace paths — API changes in Phase 2 will surface observer data for future pages or API consumers.
+
+### Phase 7: Tests
+
+**`tests/test_collector/test_letsmesh_normalizer.py`**
+- Test type 4 packet extracts `snr` (lowercase) and `path_len` from envelope
+- Test both `"SNR"` and `"snr"` input casing normalizes to lowercase `"snr"` output
+- Test message payload also outputs lowercase `"snr"` (verifies line 160 casing fix)
+
+**`tests/test_collector/test_handlers/test_advertisement.py`**
+- Test handler with `snr` and `path_len` in payload → stored in `event_observers`
+
+**`tests/test_collector/test_handlers/test_message.py`**
+- Test handler passes `path_len` to `add_event_observer()`
+- Fix casing: change `"SNR": 15.5` → `"snr": 15.5` (line 21) and `"SNR": 8.5` → `"snr": 8.5` (line 102)
+
+**`tests/test_collector/test_handlers/test_trace.py`**
+- Test handler with envelope `snr`/`path_len` → stored in `event_observers`
+
+**`tests/test_collector/test_handlers/test_telemetry.py`**
+- Test handler with envelope `snr`/`path_len` → stored in `event_observers`
+
+**`tests/test_common/test_models.py`**
+- Test `add_event_observer()` accepts and stores `path_len`
+- Test backwards compatibility (`path_len=None` is default)
+
+**`tests/test_api/test_trace_paths.py`**
+- Test `observers` list is populated (query returns data)
+
+**`tests/test_api/test_telemetry.py`**
+- Test `observers` list is populated (query returns data)
+
+**Run commands:**
+```bash
+source .venv/bin/activate
+pytest tests/test_collector/ -v
+pytest tests/test_api/ -v
+pytest tests/test_common/ -v
+pre-commit run --all-files
+```
+
+### Phase 8: Documentation
+
+**`SCHEMAS.md`:**
+- Document that `SNR` and `path` are LetsMesh envelope fields available on all packet types
+- Update `ObserverInfo` description to include `path_len`
+
+**`AGENTS.md`:**
+- Update `event_observers` table description to include `path_len` column
+
+---
+
+## File Change Summary
+
+| # | File | Action | Phase |
+|---|------|--------|-------|
+| 1 | `common/models/event_observer.py` | Modify | 1 |
+| 2 | `alembic/versions/*.py` | Create | 1 |
+| 3 | `common/schemas/messages.py` | Modify | 2 |
+| 4 | `api/observer_utils.py` | Create | 2 |
+| 5 | `api/routes/messages.py` | Modify | 2 |
+| 6 | `api/routes/advertisements.py` | Modify | 2 |
+| 7 | `api/routes/trace_paths.py` | Modify | 2 |
+| 8 | `api/routes/telemetry.py` | Modify | 2 |
+| 9 | `collector/letsmesh_normalizer.py` | Modify | 3 |
+| 10 | `collector/handlers/message.py` | Modify | 4 |
+| 11 | `collector/handlers/advertisement.py` | Modify | 4 |
+| 12 | `collector/handlers/trace.py` | Modify | 4 |
+| 13 | `collector/handlers/telemetry.py` | Modify | 4 |
+| 14 | `web/static/js/spa/components.js` | Modify | 5 |
+| 15 | `web/static/css/app.css` | Modify | 5 |
+| 16 | `web/static/js/spa/pages/messages.js` | Modify | 6 |
+| 17 | `web/static/js/spa/pages/advertisements.js` | Modify | 6 |
+| 18 | `SCHEMAS.md` | Modify | 8 |
+| 19 | `AGENTS.md` | Modify | 8 |
+
+---
+
+## Source Files Reference
+
+| File | Key Locations |
+|------|--------------|
+| `common/models/event_observer.py` | `EventObserver` model, `add_event_observer()` helper |
+| `common/hash_utils.py` | Hash computation for deduplication |
+| `common/schemas/messages.py` | `ObserverInfo`, `MessageRead`, `AdvertisementRead`, `TracePathRead`, `TelemetryRead` |
+| `collector/letsmesh_normalizer.py` | `_build_letsmesh_advertisement_payload()` (line 544), `_build_letsmesh_message_payload()` (line 84) |
+| `collector/handlers/advertisement.py` | 3x `add_event_observer()` at lines 120, 182, 203 |
+| `collector/handlers/message.py` | 3x `add_event_observer()` at lines 124, 158, 178 |
+| `collector/handlers/trace.py` | 3x `add_event_observer()` at lines 74, 106, 126 |
+| `collector/handlers/telemetry.py` | 3x `add_event_observer()` at lines 87, 133, 154 |
+| `api/routes/messages.py` | `_fetch_observers_for_events()` at line 28 |
+| `api/routes/advertisements.py` | `_fetch_observers_for_events()` at line 42 |
+| `api/routes/trace_paths.py` | Returns `[]` for observers |
+| `api/routes/telemetry.py` | Returns `[]` for observers |
+| `web/static/js/spa/components.js` | Dead `receiverIcons()` at line 444 |
+| `web/static/js/spa/pages/messages.js` | Observer rendering at lines 206-216 (mobile), 255-267 (desktop) |
+| `web/static/js/spa/pages/advertisements.js` | Observer rendering at lines 99-109 (mobile), 135-147 (desktop) |
@@ -0,0 +1,127 @@
+# Observer Detail Rows — Task Checklist
+
+**Plan:** `docs/plans/20260426-1137-improve-snr-path-visibility/plan.md`
+**Status:** Complete
+
+## Review Notes
+
+> **Plan accuracy issue found:** Phase 4 changes `message.py` handler to read only `payload.get("snr")` (lowercase), but the LetsMesh **message** normalizer (`letsmesh_normalizer.py:160`) still outputs `normalized_payload["SNR"]` (uppercase). Phase 3 only fixes the **advertisement** normalizer. An additional task (Phase 3.5) is included below to normalize the message normalizer output to lowercase `"snr"`, consistent with Decision #2.
+
+---
+
+## Phase 1: Database Schema
+
+- [x] **1.1** Add `path_len: Mapped[Optional[int]] = mapped_column(Integer, nullable=True)` to `EventObserver` model in `src/meshcore_hub/common/models/event_observer.py`
+- [x] **1.2** Add `path_len: Optional[int] = None` parameter to `add_event_observer()` signature
+- [x] **1.3** Include `path_len=path_len` in `sqlite_insert().values()` call
+- [x] **1.4** Generate Alembic migration: `meshcore-hub db revision --autogenerate -m "add path_len to event_observers"`
+- [x] **1.5** Review and adjust migration file
+- [x] **1.6** Run migration: `meshcore-hub db upgrade`
+
+## Phase 2: API Utility & Schema
+
+- [x] **2.1** Add `path_len: Optional[int] = Field(default=None, description="Hop count at this observer")` to `ObserverInfo` schema in `src/meshcore_hub/common/schemas/messages.py`
+- [x] **2.2** Create `src/meshcore_hub/api/observer_utils.py` — move shared `_fetch_observers_for_events()` function
+- [x] **2.3** Update shared query to also select `EventObserver.path_len`
+- [x] **2.4** Include `path_len=row.path_len` in `ObserverInfo()` construction within the shared function
+- [x] **2.5** Update `api/routes/messages.py` — remove local `_fetch_observers_for_events`, import from `observer_utils`; also remove local `_get_tag_name` if it becomes unused
+- [x] **2.6** Update `api/routes/advertisements.py` — same as 2.5
+- [x] **2.7** Update `api/routes/trace_paths.py` — import and call `_fetch_observers_for_events(session, "trace", event_hashes)` for both list and detail endpoints; include `"observers"` key in response dicts
+- [x] **2.8** Update `api/routes/telemetry.py` — same pattern as 2.7 with `"telemetry"` event type
+
+## Phase 3: LetsMesh Normalizer — Advertisement SNR & Path
+
+- [x] **3.1** In `src/meshcore_hub/collector/letsmesh_normalizer.py`, in `_build_letsmesh_advertisement_payload()`, add SNR extraction after `normalized_payload` dict initialization (~line 574): `snr = self._parse_float(payload.get("SNR"))`, fallback to `payload.get("snr")`, store as `normalized_payload["snr"]` (lowercase)
+- [x] **3.2** Add `path_len = self._parse_path_length(payload.get("path"))` extraction, store as `normalized_payload["path_len"]`
+- [x] **3.3** Return the updated `normalized_payload` (already returned at line 627)
+
+## Phase 3.5: LetsMesh Normalizer — Message SNR Casing Fix
+
+> **Accuracy fix:** Not in original plan. Required to prevent SNR data loss for LetsMesh-routed messages after Phase 4 removes the uppercase fallback.
+
+- [x] **3.5.1** In `src/meshcore_hub/collector/letsmesh_normalizer.py`, change line 160: `normalized_payload["SNR"]` → `normalized_payload["snr"]` (lowercase, per Decision #2)
+
+## Phase 4: Collector Handlers
+
+- [x] **4.1** `src/meshcore_hub/collector/handlers/message.py` — change line 78: `payload.get("SNR") or payload.get("snr")` → `payload.get("snr")`
+- [x] **4.2** `message.py` — pass `path_len=path_len` to all 3 `add_event_observer()` call sites (lines 124, 158, 178)
+- [x] **4.3** `src/meshcore_hub/collector/handlers/advertisement.py` — add extraction: `snr = payload.get("snr")` and `path_len = payload.get("path_len")`
+- [x] **4.4** `advertisement.py` — pass `snr=snr, path_len=path_len` to all 3 `add_event_observer()` call sites (lines 120, 182, 203); replace current `snr=None`
+- [x] **4.5** `src/meshcore_hub/collector/handlers/trace.py` — add extraction: `snr = payload.get("snr")`
+- [x] **4.6** `trace.py` — pass `snr=snr, path_len=path_len` to all 3 `add_event_observer()` call sites (lines 74, 106, 126); replace current `snr=None`
+- [x] **4.7** `src/meshcore_hub/collector/handlers/telemetry.py` — add extraction: `snr = payload.get("snr")` and `path_len = payload.get("path_len")`
+- [x] **4.8** `telemetry.py` — pass `snr=snr, path_len=path_len` to all 3 `add_event_observer()` call sites (lines 87, 133, 154); replace current `snr=None`
+
+## Phase 5: Frontend Components
+
+- [x] **5.1** Remove dead `receiverIcons()` function from `src/meshcore_hub/web/static/js/spa/components.js` (lines 444-452)
+- [x] **5.2** Add `observerDetailRow(observers, eventProperties)` component to `components.js`:
+  - Renders expandable sub-table with columns: Observer (name/link), SNR (formatted dB), Path (formatted hops), Received (relative time)
+  - `eventProperties` param for event-level context (e.g., trace `snr_values`)
+  - Toggle helper: click event row to show/hide `.observer-detail` row
+- [x] **5.3** Add `observerIcons(observers)` component — count badge with tooltip listing observer names
+- [x] **5.4** Add `.observer-detail` expandable row styles to `src/meshcore_hub/web/static/css/app.css`:
+  - Indented, compact sub-table styling
+  - CSS transition for smooth expand/collapse (max-height animation)
+  - Responsive: desktop table vs mobile card layout
+
+## Phase 6: Frontend Pages
+
+- [x] **6.1** Update `src/meshcore_hub/web/static/js/spa/pages/messages.js`:
+  - Replace satellite dish icon rendering with observer count badge (clickable to expand)
+  - Add expandable detail row showing per-observer: name, SNR, path_len, observed_at
+  - Update both mobile card view (~line 206) and desktop table view (~line 255)
+- [x] **6.2** Update `src/meshcore_hub/web/static/js/spa/pages/advertisements.js`:
+  - Same pattern as messages
+  - Update both mobile card view (~line 99) and desktop table view (~line 135)
+
+## Phase 7: Tests
+
+- [x] **7.1** `tests/test_collector/test_letsmesh_normalizer.py` — test type 4 packet extracts `snr` (lowercase) and `path_len` from envelope
+- [x] **7.2** `tests/test_collector/test_letsmesh_normalizer.py` — test both `"SNR"` and `"snr"` input casing normalizes to lowercase `"snr"` output
+- [x] **7.3** `tests/test_collector/test_letsmesh_normalizer.py` — test message payload also outputs lowercase `"snr"` (verifies Phase 3.5 fix)
+- [x] **7.4** `tests/test_collector/test_handlers/test_advertisement.py` — test handler with `snr` and `path_len` in payload → stored in `event_observers`
+- [x] **7.5** `tests/test_collector/test_handlers/test_message.py` — test handler passes `path_len` to `add_event_observer()`
+- [x] **7.6** `tests/test_collector/test_handlers/test_message.py` — fix casing: `"SNR": 15.5` → `"snr": 15.5` (line 21) and `"SNR": 8.5` → `"snr": 8.5` (line 102)
+- [x] **7.7** `tests/test_collector/test_handlers/test_trace.py` — test handler with envelope `snr`/`path_len` → stored in `event_observers`
+- [x] **7.8** `tests/test_collector/test_handlers/test_telemetry.py` — test handler with envelope `snr`/`path_len` → stored in `event_observers`
+- [x] **7.9** `tests/test_common/test_models.py` — test `add_event_observer()` accepts and stores `path_len`
+- [x] **7.10** `tests/test_common/test_models.py` — test backwards compatibility (`path_len=None` is default)
+- [x] **7.11** `tests/test_api/test_trace_paths.py` — test `observers` list is populated (query returns data)
+- [x] **7.12** `tests/test_api/test_telemetry.py` — test `observers` list is populated (query returns data)
+- [x] **7.13** Run targeted tests: `pytest tests/test_collector/ -v`
+- [x] **7.14** Run targeted tests: `pytest tests/test_api/ -v`
+- [x] **7.15** Run targeted tests: `pytest tests/test_common/ -v`
+- [x] **7.16** Run quality checks: `pre-commit run --all-files`
+
+## Phase 8: Documentation
+
+- [x] **8.1** Update `SCHEMAS.md` — document that `SNR` and `path` are LetsMesh envelope fields available on all packet types
+- [x] **8.2** Update `SCHEMAS.md` — update `ObserverInfo` description to include `path_len`
+- [x] **8.3** Update `AGENTS.md` — update `event_observers` table description to include `path_len` column
+
+---
+
+## File Change Summary
+
+| # | File | Action | Phase(s) |
+|---|------|--------|----------|
+| 1 | `common/models/event_observer.py` | Modify | 1 |
+| 2 | `alembic/versions/*.py` | Create | 1 |
+| 3 | `common/schemas/messages.py` | Modify | 2 |
+| 4 | `api/observer_utils.py` | Create | 2 |
+| 5 | `api/routes/messages.py` | Modify | 2 |
+| 6 | `api/routes/advertisements.py` | Modify | 2 |
+| 7 | `api/routes/trace_paths.py` | Modify | 2 |
+| 8 | `api/routes/telemetry.py` | Modify | 2 |
+| 9 | `collector/letsmesh_normalizer.py` | Modify | 3, 3.5 |
+| 10 | `collector/handlers/message.py` | Modify | 4 |
+| 11 | `collector/handlers/advertisement.py` | Modify | 4 |
+| 12 | `collector/handlers/trace.py` | Modify | 4 |
+| 13 | `collector/handlers/telemetry.py` | Modify | 4 |
+| 14 | `web/static/js/spa/components.js` | Modify | 5 |
+| 15 | `web/static/css/app.css` | Modify | 5 |
+| 16 | `web/static/js/spa/pages/messages.js` | Modify | 6 |
+| 17 | `web/static/js/spa/pages/advertisements.js` | Modify | 6 |
+| 18 | `SCHEMAS.md` | Modify | 8 |
+| 19 | `AGENTS.md` | Modify | 8 |
@@ -0,0 +1,75 @@
+"""Shared utilities for fetching event observer data."""
+
+from sqlalchemy import select
+
+from meshcore_hub.api.dependencies import DbSession
+from meshcore_hub.common.models import EventObserver, Node, NodeTag
+from meshcore_hub.common.schemas.messages import ObserverInfo
+
+
+def fetch_observers_for_events(
+    session: DbSession,
+    event_type: str,
+    event_hashes: list[str],
+) -> dict[str, list[ObserverInfo]]:
+    """Fetch observer info for a list of events by their hashes.
+
+    Args:
+        session: Database session
+        event_type: Type of event ('message', 'advertisement', etc.)
+        event_hashes: List of event hashes to fetch observers for
+
+    Returns:
+        Dict mapping event_hash to list of ObserverInfo objects
+    """
+    if not event_hashes:
+        return {}
+
+    query = (
+        select(
+            EventObserver.event_hash,
+            EventObserver.snr,
+            EventObserver.path_len,
+            EventObserver.observed_at,
+            Node.id.label("node_id"),
+            Node.public_key,
+            Node.name,
+        )
+        .join(Node, EventObserver.observer_node_id == Node.id)
+        .where(EventObserver.event_type == event_type)
+        .where(EventObserver.event_hash.in_(event_hashes))
+        .order_by(EventObserver.observed_at)
+    )
+
+    results = session.execute(query).all()
+
+    observers_by_hash: dict[str, list[ObserverInfo]] = {}
+
+    node_ids = [r.node_id for r in results]
+    tag_names: dict[str, str] = {}
+    if node_ids:
+        tag_query = (
+            select(NodeTag.node_id, NodeTag.value)
+            .where(NodeTag.node_id.in_(node_ids))
+            .where(NodeTag.key == "name")
+        )
+        for node_id, value in session.execute(tag_query).all():
+            tag_names[node_id] = value
+
+    for row in results:
+        if row.event_hash not in observers_by_hash:
+            observers_by_hash[row.event_hash] = []
+
+        observers_by_hash[row.event_hash].append(
+            ObserverInfo(
+                node_id=row.node_id,
+                public_key=row.public_key,
+                name=row.name,
+                tag_name=tag_names.get(row.node_id),
+                snr=row.snr,
+                path_len=row.path_len,
+                observed_at=row.observed_at,
+            )
+        )
+
+    return observers_by_hash
@@ -9,11 +9,11 @@ from sqlalchemy.orm import aliased, selectinload

 from meshcore_hub.api.auth import RequireRead
 from meshcore_hub.api.dependencies import DbSession
-from meshcore_hub.common.models import Advertisement, EventObserver, Node, NodeTag
+from meshcore_hub.api.observer_utils import fetch_observers_for_events
+from meshcore_hub.common.models import Advertisement, Node, NodeTag
 from meshcore_hub.common.schemas.messages import (
    AdvertisementList,
    AdvertisementRead,
-    ObserverInfo,
 )

 router = APIRouter()
@@ -39,62 +39,6 @@ def _get_tag_description(node: Optional[Node]) -> Optional[str]:
    return None


-def _fetch_observers_for_events(
-    session: DbSession,
-    event_type: str,
-    event_hashes: list[str],
-) -> dict[str, list[ObserverInfo]]:
-    """Fetch receiver info for a list of events by their hashes."""
-    if not event_hashes:
-        return {}
-
-    query = (
-        select(
-            EventObserver.event_hash,
-            EventObserver.snr,
-            EventObserver.observed_at,
-            Node.id.label("node_id"),
-            Node.public_key,
-            Node.name,
-        )
-        .join(Node, EventObserver.observer_node_id == Node.id)
-        .where(EventObserver.event_type == event_type)
-        .where(EventObserver.event_hash.in_(event_hashes))
-        .order_by(EventObserver.observed_at)
-    )
-
-    results = session.execute(query).all()
-    observers_by_hash: dict[str, list[ObserverInfo]] = {}
-
-    node_ids = [r.node_id for r in results]
-    tag_names: dict[str, str] = {}
-    if node_ids:
-        tag_query = (
-            select(NodeTag.node_id, NodeTag.value)
-            .where(NodeTag.node_id.in_(node_ids))
-            .where(NodeTag.key == "name")
-        )
-        for node_id, value in session.execute(tag_query).all():
-            tag_names[node_id] = value
-
-    for row in results:
-        if row.event_hash not in observers_by_hash:
-            observers_by_hash[row.event_hash] = []
-
-        observers_by_hash[row.event_hash].append(
-            ObserverInfo(
-                node_id=row.node_id,
-                public_key=row.public_key,
-                name=row.name,
-                tag_name=tag_names.get(row.node_id),
-                snr=row.snr,
-                observed_at=row.observed_at,
-            )
-        )
-
-    return observers_by_hash
-
-
@router.get("", response_model=AdvertisementList)
 async def list_advertisements(
    _: RequireRead,
@@ -201,7 +145,7 @@ async def list_advertisements(

    # Fetch all observers for these advertisements
    event_hashes = [r[0].event_hash for r in results if r[0].event_hash]
-    observers_by_hash = _fetch_observers_for_events(
+    observers_by_hash = fetch_observers_for_events(
        session, "advertisement", event_hashes
    )

@@ -290,7 +234,7 @@ async def get_advertisement(
    # Fetch observers for this advertisement
    observers = []
    if adv.event_hash:
-        observers_by_hash = _fetch_observers_for_events(
+        observers_by_hash = fetch_observers_for_events(
            session, "advertisement", [adv.event_hash]
        )
        observers = observers_by_hash.get(adv.event_hash, [])
@@ -9,8 +9,9 @@ from sqlalchemy.orm import aliased, selectinload

 from meshcore_hub.api.auth import RequireRead
 from meshcore_hub.api.dependencies import DbSession
-from meshcore_hub.common.models import EventObserver, Message, Node, NodeTag
-from meshcore_hub.common.schemas.messages import MessageList, MessageRead, ObserverInfo
+from meshcore_hub.api.observer_utils import fetch_observers_for_events
+from meshcore_hub.common.models import Message, Node, NodeTag
+from meshcore_hub.common.schemas.messages import MessageList, MessageRead

 router = APIRouter()

@@ -25,75 +26,6 @@ def _get_tag_name(node: Optional[Node]) -> Optional[str]:
    return None


-def _fetch_observers_for_events(
-    session: DbSession,
-    event_type: str,
-    event_hashes: list[str],
-) -> dict[str, list[ObserverInfo]]:
-    """Fetch receiver info for a list of events by their hashes.
-
-    Args:
-        session: Database session
-        event_type: Type of event ('message', 'advertisement', etc.)
-        event_hashes: List of event hashes to fetch observers for
-
-    Returns:
-        Dict mapping event_hash to list of ObserverInfo objects
-    """
-    if not event_hashes:
-        return {}
-
-    # Query event_observers with receiver node info
-    query = (
-        select(
-            EventObserver.event_hash,
-            EventObserver.snr,
-            EventObserver.observed_at,
-            Node.id.label("node_id"),
-            Node.public_key,
-            Node.name,
-        )
-        .join(Node, EventObserver.observer_node_id == Node.id)
-        .where(EventObserver.event_type == event_type)
-        .where(EventObserver.event_hash.in_(event_hashes))
-        .order_by(EventObserver.observed_at)
-    )
-
-    results = session.execute(query).all()
-
-    # Group by event_hash
-    observers_by_hash: dict[str, list[ObserverInfo]] = {}
-
-    # Get tag names for receiver nodes
-    node_ids = [r.node_id for r in results]
-    tag_names: dict[str, str] = {}
-    if node_ids:
-        tag_query = (
-            select(NodeTag.node_id, NodeTag.value)
-            .where(NodeTag.node_id.in_(node_ids))
-            .where(NodeTag.key == "name")
-        )
-        for node_id, value in session.execute(tag_query).all():
-            tag_names[node_id] = value
-
-    for row in results:
-        if row.event_hash not in observers_by_hash:
-            observers_by_hash[row.event_hash] = []
-
-        observers_by_hash[row.event_hash].append(
-            ObserverInfo(
-                node_id=row.node_id,
-                public_key=row.public_key,
-                name=row.name,
-                tag_name=tag_names.get(row.node_id),
-                snr=row.snr,
-                observed_at=row.observed_at,
-            )
-        )
-
-    return observers_by_hash
-
-
@router.get("", response_model=MessageList)
 async def list_messages(
    _: RequireRead,
@@ -197,7 +129,7 @@ async def list_messages(

    # Fetch all observers for these messages
    event_hashes = [r[0].event_hash for r in results if r[0].event_hash]
-    observers_by_hash = _fetch_observers_for_events(session, "message", event_hashes)
+    observers_by_hash = fetch_observers_for_events(session, "message", event_hashes)

    # Build response with sender info and observed_by
    items = []
@@ -269,7 +201,7 @@ async def get_message(
    # Fetch observers for this message
    observers = []
    if message.event_hash:
-        observers_by_hash = _fetch_observers_for_events(
+        observers_by_hash = fetch_observers_for_events(
            session, "message", [message.event_hash]
        )
        observers = observers_by_hash.get(message.event_hash, [])
@@ -9,6 +9,7 @@ from sqlalchemy.orm import aliased

 from meshcore_hub.api.auth import RequireRead
 from meshcore_hub.api.dependencies import DbSession
+from meshcore_hub.api.observer_utils import fetch_observers_for_events
 from meshcore_hub.common.models import Node, Telemetry
 from meshcore_hub.common.schemas.messages import TelemetryList, TelemetryRead

@@ -59,6 +60,10 @@ async def list_telemetry(
    # Execute
    results = session.execute(query).all()

+    # Fetch observers for these telemetry records
+    event_hashes = [tel.event_hash for tel, _ in results if tel.event_hash]
+    observers_by_hash = fetch_observers_for_events(session, "telemetry", event_hashes)
+
    # Build response with observed_by
    items = []
    for tel, observer_pk in results:
@@ -71,6 +76,9 @@ async def list_telemetry(
            "parsed_data": tel.parsed_data,
            "received_at": tel.received_at,
            "created_at": tel.created_at,
+            "observers": (
+                observers_by_hash.get(tel.event_hash, []) if tel.event_hash else []
+            ),
        }
        items.append(TelemetryRead(**data))

@@ -101,6 +109,14 @@ async def get_telemetry(
        raise HTTPException(status_code=404, detail="Telemetry record not found")

    tel, observer_pk = result
+
+    observers = []
+    if tel.event_hash:
+        observers_by_hash = fetch_observers_for_events(
+            session, "telemetry", [tel.event_hash]
+        )
+        observers = observers_by_hash.get(tel.event_hash, [])
+
    data = {
        "id": tel.id,
        "observer_node_id": tel.observer_node_id,
@@ -110,5 +126,6 @@ async def get_telemetry(
        "parsed_data": tel.parsed_data,
        "received_at": tel.received_at,
        "created_at": tel.created_at,
+        "observers": observers,
    }
    return TelemetryRead(**data)
@@ -9,6 +9,7 @@ from sqlalchemy.orm import aliased

 from meshcore_hub.api.auth import RequireRead
 from meshcore_hub.api.dependencies import DbSession
+from meshcore_hub.api.observer_utils import fetch_observers_for_events
 from meshcore_hub.common.models import Node, TracePath
 from meshcore_hub.common.schemas.messages import TracePathList, TracePathRead

@@ -55,6 +56,10 @@ async def list_trace_paths(
    # Execute
    results = session.execute(query).all()

+    # Fetch observers for these trace paths
+    event_hashes = [tp.event_hash for tp, _ in results if tp.event_hash]
+    observers_by_hash = fetch_observers_for_events(session, "trace", event_hashes)
+
    # Build response with observed_by
    items = []
    for tp, observer_pk in results:
@@ -71,6 +76,9 @@ async def list_trace_paths(
            "hop_count": tp.hop_count,
            "received_at": tp.received_at,
            "created_at": tp.created_at,
+            "observers": (
+                observers_by_hash.get(tp.event_hash, []) if tp.event_hash else []
+            ),
        }
        items.append(TracePathRead(**data))

@@ -101,6 +109,14 @@ async def get_trace_path(
        raise HTTPException(status_code=404, detail="Trace path not found")

    tp, observer_pk = result
+
+    observers = []
+    if tp.event_hash:
+        observers_by_hash = fetch_observers_for_events(
+            session, "trace", [tp.event_hash]
+        )
+        observers = observers_by_hash.get(tp.event_hash, [])
+
    data = {
        "id": tp.id,
        "observer_node_id": tp.observer_node_id,
@@ -114,5 +130,6 @@ async def get_trace_path(
        "hop_count": tp.hop_count,
        "received_at": tp.received_at,
        "created_at": tp.created_at,
+        "observers": observers,
    }
    return TracePathRead(**data)
@@ -72,6 +72,9 @@ def handle_advertisement(
    lon = _coerce_float(lon)
    now = datetime.now(timezone.utc)

+    snr = payload.get("snr")
+    path_len = payload.get("path_len")
+
    # Compute event hash for deduplication (30-second time bucket)
    event_hash = compute_advertisement_hash(
        public_key=adv_public_key,
@@ -122,7 +125,8 @@ def handle_advertisement(
                    event_type="advertisement",
                    event_hash=event_hash,
                    observer_node_id=receiver_node.id,
-                    snr=None,  # Advertisements don't have SNR
+                    snr=snr,
+                    path_len=path_len,
                    observed_at=now,
                )
                if added:
@@ -184,7 +188,8 @@ def handle_advertisement(
                event_type="advertisement",
                event_hash=event_hash,
                observer_node_id=receiver_node.id,
-                snr=None,
+                snr=snr,
+                path_len=path_len,
                observed_at=now,
            )

@@ -205,7 +210,8 @@ def handle_advertisement(
                    event_type="advertisement",
                    event_hash=event_hash,
                    observer_node_id=receiver_node.id,
-                    snr=None,
+                    snr=snr,
+                    path_len=path_len,
                    observed_at=now,
                )
            return
@@ -75,7 +75,7 @@ def _handle_message(
    path_len = payload.get("path_len")
    txt_type = payload.get("txt_type")
    signature = payload.get("signature")
-    snr = payload.get("SNR") or payload.get("snr")
+    snr = payload.get("snr")

    # Parse sender timestamp
    sender_ts = payload.get("sender_timestamp")
@@ -127,6 +127,7 @@ def _handle_message(
                    event_hash=event_hash,
                    observer_node_id=receiver_node.id,
                    snr=snr,
+                    path_len=path_len,
                    observed_at=now,
                )
                if added:
@@ -161,6 +162,7 @@ def _handle_message(
                event_hash=event_hash,
                observer_node_id=receiver_node.id,
                snr=snr,
+                path_len=path_len,
                observed_at=now,
            )

@@ -181,6 +183,7 @@ def _handle_message(
                    event_hash=event_hash,
                    observer_node_id=receiver_node.id,
                    snr=snr,
+                    path_len=path_len,
                    observed_at=now,
                )
            return
@@ -37,6 +37,8 @@ def handle_telemetry(

    lpp_data = payload.get("lpp_data")
    parsed_data = payload.get("parsed_data")
+    snr = payload.get("snr")
+    path_len = payload.get("path_len")

    # Convert lpp_data to bytes if it's a string or list
    lpp_bytes = None
@@ -89,7 +91,8 @@ def handle_telemetry(
                    event_type="telemetry",
                    event_hash=event_hash,
                    observer_node_id=receiver_node.id,
-                    snr=None,
+                    snr=snr,
+                    path_len=path_len,
                    observed_at=now,
                )
                if added:
@@ -135,7 +138,8 @@ def handle_telemetry(
                event_type="telemetry",
                event_hash=event_hash,
                observer_node_id=receiver_node.id,
-                snr=None,
+                snr=snr,
+                path_len=path_len,
                observed_at=now,
            )

@@ -156,7 +160,8 @@ def handle_telemetry(
                    event_type="telemetry",
                    event_hash=event_hash,
                    observer_node_id=receiver_node.id,
-                    snr=None,
+                    snr=snr,
+                    path_len=path_len,
                    observed_at=now,
                )
            return
@@ -41,6 +41,7 @@ def handle_trace_data(
    path_hashes = payload.get("path_hashes")
    snr_values = payload.get("snr_values")
    hop_count = payload.get("hop_count")
+    snr = payload.get("snr")

    # Compute event hash for deduplication (initiator_tag is unique per trace)
    event_hash = compute_trace_hash(initiator_tag=initiator_tag)
@@ -76,7 +77,8 @@ def handle_trace_data(
                    event_type="trace",
                    event_hash=event_hash,
                    observer_node_id=receiver_node.id,
-                    snr=None,  # Trace events don't have a single SNR value
+                    snr=snr,
+                    path_len=path_len,
                    observed_at=now,
                )
                if added:
@@ -108,7 +110,8 @@ def handle_trace_data(
                event_type="trace",
                event_hash=event_hash,
                observer_node_id=receiver_node.id,
-                snr=None,
+                snr=snr,
+                path_len=path_len,
                observed_at=now,
            )

@@ -128,7 +131,8 @@ def handle_trace_data(
                    event_type="trace",
                    event_hash=event_hash,
                    observer_node_id=receiver_node.id,
-                    snr=None,
+                    snr=snr,
+                    path_len=path_len,
                    observed_at=now,
                )
            return
@@ -157,7 +157,8 @@ class LetsMeshNormalizer:
        if snr is None:
            snr = self._parse_float(payload.get("snr"))
        if snr is not None:
-            normalized_payload["SNR"] = snr
+            normalized_payload["snr"] = snr
+        normalized_payload.pop("SNR", None)

        decoded_sender = self._extract_letsmesh_decoder_sender(
            decoded_packet,
@@ -575,6 +576,16 @@ class LetsMeshNormalizer:
            "public_key": public_key,
        }

+        snr = self._parse_float(payload.get("SNR"))
+        if snr is None:
+            snr = self._parse_float(payload.get("snr"))
+        if snr is not None:
+            normalized_payload["snr"] = snr
+
+        path_len = self._parse_path_length(payload.get("path"))
+        if path_len is not None:
+            normalized_payload["path_len"] = path_len
+
        app_data = decoded_payload.get("appData")
        if isinstance(app_data, dict):
            name = app_data.get("name")
@@ -4,7 +4,15 @@ from datetime import datetime
 from typing import TYPE_CHECKING, Optional
 from uuid import uuid4

-from sqlalchemy import DateTime, Float, ForeignKey, Index, String, UniqueConstraint
+from sqlalchemy import (
+    DateTime,
+    Float,
+    ForeignKey,
+    Integer,
+    Index,
+    String,
+    UniqueConstraint,
+)
 from sqlalchemy.dialects.sqlite import insert as sqlite_insert
 from sqlalchemy.orm import Mapped, Session, mapped_column, relationship

@@ -27,6 +35,7 @@ class EventObserver(Base, UUIDMixin, TimestampMixin):
        event_hash: Hash identifying the unique event (links to event tables)
        observer_node_id: FK to the node that observed this event
        snr: Signal-to-noise ratio at this observer (if available)
+        path_len: Hop count at this observer (if available)
        observed_at: When this specific observer captured the event
        created_at: Record creation timestamp
        updated_at: Record update timestamp
@@ -53,6 +62,10 @@ class EventObserver(Base, UUIDMixin, TimestampMixin):
        Float,
        nullable=True,
    )
+    path_len: Mapped[Optional[int]] = mapped_column(
+        Integer,
+        nullable=True,
+    )
    observed_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True),
        default=utc_now,
@@ -85,6 +98,7 @@ def add_event_observer(
    event_hash: str,
    observer_node_id: str,
    snr: Optional[float] = None,
+    path_len: Optional[int] = None,
    observed_at: Optional[datetime] = None,
 ) -> bool:
    """Add an observer to an event, handling duplicates gracefully.
@@ -97,6 +111,7 @@ def add_event_observer(
        event_hash: Hash identifying the unique event
        observer_node_id: UUID of the observer node
        snr: Signal-to-noise ratio at this observer (optional)
+        path_len: Hop count at this observer (optional)
        observed_at: When this observer captured the event (defaults to now)

    Returns:
@@ -114,6 +129,7 @@ def add_event_observer(
            event_hash=event_hash,
            observer_node_id=observer_node_id,
            snr=snr,
+            path_len=path_len,
            observed_at=now,
            created_at=now,
            updated_at=now,
@@ -16,6 +16,9 @@ class ObserverInfo(BaseModel):
    snr: Optional[float] = Field(
        default=None, description="Signal-to-noise ratio at this observer"
    )
+    path_len: Optional[int] = Field(
+        default=None, description="Hop count at this observer"
+    )
    observed_at: datetime = Field(
        ..., description="When this observer captured the event"
    )
@@ -348,3 +348,41 @@
 #header-map .leaflet-control {
    z-index: auto !important;
 }
+
+/* ==========================================================================
+   Observer Detail Rows
+   Expandable sub-table showing per-observer signal/path data.
+   ========================================================================== */
+
+.observer-detail .observer-detail-content {
+    padding: 0.5rem 1rem 0.5rem 2rem;
+}
+
+.observer-detail table {
+    margin: 0;
+}
+
+.observer-badge {
+    transition: background-color 0.15s ease;
+}
+
+.observer-badge:hover {
+    background-color: color-mix(in oklch, var(--color-base-content) 15%, transparent);
+}
+
+.observer-badge-group {
+    display: inline-flex;
+    align-items: center;
+    gap: 0.25rem;
+}
+
+/* Mobile card observer details */
+.observer-detail-card {
+    padding: 0.5rem 0.75rem;
+    margin-top: 0.25rem;
+}
+
+.observer-detail-card table {
+    margin: 0;
+    font-size: 0.8rem;
+}
@@ -437,18 +437,83 @@ export function timezoneIndicator() {
 }

 /**
- * Render receiver node icons with tooltips.
- * @param {Array} receivers
+ * Render an observer count badge with tooltip listing observer names.
+ * @param {Array} observers - Array of observer objects
 * @returns {TemplateResult|nothing}
 */
-export function receiverIcons(receivers) {
-    if (!receivers || receivers.length === 0) return nothing;
-    return html`${receivers.map(r => {
-        const name = r.receiver_node_name || truncateKey(r.receiver_node_public_key || '', 8);
-        const time = formatRelativeTime(r.received_at);
-        const tooltip = time ? `${name} (${time})` : name;
-        return html`<span class="cursor-help" title=${tooltip}>\u{1F4E1}</span>`;
-    })}`;
+export function observerIcons(observers) {
+    if (!observers || observers.length === 0) return nothing;
+    const names = observers.map(o => o.tag_name || o.name || truncateKey(o.public_key, 8));
+    const tooltip = names.join(', ');
+    return html`<span class="observer-badge-group">\u{1F4E1}<span class="badge badge-sm badge-ghost cursor-help observer-badge" title=${tooltip}>${observers.length}</span></span>`;
+}
+
+/**
+ * Render an expandable observer detail row.
+ * Shows per-observer: name, SNR, path_len, observed_at.
+ * @param {Array} observers - Array of observer objects
+ * @param {Object} [eventProperties] - Event-level context (unused, for future use)
+ * @returns {TemplateResult|nothing}
+ */
+export function observerDetailRow(observers, eventProperties, options = {}) {
+    if (!observers || observers.length === 0) return nothing;
+    const showPath = !options.hidePath;
+    return html`
+        <tr class="observer-detail hidden">
+            <td colspan="100" class="p-0">
+                <div class="observer-detail-content">
+                    <table class="table table-xs w-full">
+                        <thead>
+                            <tr>
+                                <th>Observer</th>
+                                <th>SNR</th>
+                                ${showPath ? html`<th>Path</th>` : nothing}
+                                <th>Received</th>
+                            </tr>
+                        </thead>
+                        <tbody>
+                            ${observers.map(o => {
+                                const displayName = o.tag_name || o.name || truncateKey(o.public_key, 12);
+                                const snrDisplay = o.snr != null ? `${Number(o.snr).toFixed(1)} dB` : '\u2014';
+                                const pathDisplay = o.path_len != null ? `${o.path_len} hop${o.path_len !== 1 ? 's' : ''}` : '\u2014';
+                                const timeDisplay = formatRelativeTime(o.observed_at);
+                                return html`
+                                    <tr>
+                                        <td>\u{1F4E1} <a href="/nodes/${o.public_key}" class="link link-hover">${displayName}</a></td>
+                                        <td>${snrDisplay}</td>
+                                        ${showPath ? html`<td>${pathDisplay}</td>` : nothing}
+                                        <td><span title=${formatDateTime(o.observed_at)}>${timeDisplay}</span></td>
+                                    </tr>
+                                `;
+                            })}
+                        </tbody>
+                    </table>
+                </div>
+            </td>
+        </tr>
+    `;
+}
+
+/**
+ * Toggle observer detail row visibility when clicking an event row.
+ * @param {Event} event - Click event
+ */
+export function toggleObserverDetail(event) {
+    const row = event.currentTarget;
+    const detailRow = row.nextElementSibling;
+    if (detailRow && detailRow.classList.contains('observer-detail')) {
+        detailRow.classList.toggle('hidden');
+    }
+}
+
+export function toggleCardObserverDetail(event) {
+    event.stopPropagation();
+    event.preventDefault();
+    const card = event.currentTarget.closest('.card');
+    if (card) {
+        const detail = card.querySelector('.observer-detail-card');
+        if (detail) detail.classList.toggle('hidden');
+    }
 }

 // --- Form Helpers ---
@@ -1,9 +1,10 @@
 import { apiGet } from '../api.js';
 import {
    html, litRender, nothing, t,
-    getConfig, formatDateTime, formatDateTimeShort,
+    getConfig, formatDateTime, formatDateTimeShort, formatRelativeTime,
    truncateKey, errorAlert,
-    pagination, createFilterHandler, autoSubmit, submitOnEnter, copyToClipboard, renderNodeDisplay
+    pagination, createFilterHandler, autoSubmit, submitOnEnter, copyToClipboard, renderNodeDisplay,
+    observerIcons, observerDetailRow, toggleObserverDetail, toggleCardObserverDetail
 } from '../components.js';
 import { createAutoRefresh } from '../auto-refresh.js';

@@ -98,15 +99,9 @@ ${content}`, container);
                    const adDescription = ad.node_tag_description;
                    let receiversBlock = nothing;
                    if (ad.observers && ad.observers.length >= 1) {
-                        receiversBlock = html`<div class="flex gap-0.5 justify-end mt-1">
-                            ${ad.observers.map(recv => {
-                                const recvName = recv.tag_name || recv.name || truncateKey(recv.public_key, 12);
-                                return html`<span class="text-sm" title=${recvName}>\u{1F4E1}</span>`;
-                            })}
-                        </div>`;
+                        receiversBlock = html`<span @click=${toggleCardObserverDetail} class="cursor-pointer">${observerIcons(ad.observers)}</span>`;
                    } else if (ad.observed_by) {
-                        const recvTitle = ad.observer_tag_name || ad.observer_name || truncateKey(ad.observed_by, 12);
-                        receiversBlock = html`<span class="text-sm" title=${recvTitle}>\u{1F4E1}</span>`;
+                        receiversBlock = html`<span class="opacity-50 text-xs">\u{1F4E1}</span>`;
                    }
                    return html`<a href="/nodes/${ad.public_key}" class="card bg-base-100 shadow-sm block">
            <div class="card-body p-3">
@@ -123,6 +118,25 @@ ${content}`, container);
                        ${receiversBlock}
                    </div>
                </div>
+                ${ad.observers && ad.observers.length > 0 ? html`
+                    <div class="observer-detail-card hidden mt-2">
+                        <table class="table table-xs w-full">
+                            <thead><tr><th>Observer</th><th>SNR</th><th>Received</th></tr></thead>
+                            <tbody>
+                                ${ad.observers.map(o => {
+                                    const dn = o.tag_name || o.name || truncateKey(o.public_key, 12);
+                                    const snrD = o.snr != null ? `${Number(o.snr).toFixed(1)} dB` : '\u2014';
+                                    const timeD = formatRelativeTime(o.observed_at);
+                                    return html`<tr>
+                                        <td>\u{1F4E1} <a href="/nodes/${o.public_key}" class="link link-hover">${dn}</a></td>
+                                        <td>${snrD}</td>
+                                        <td><span title=${formatDateTime(o.observed_at)}>${timeD}</span></td>
+                                    </tr>`;
+                                })}
+                            </tbody>
+                        </table>
+                    </div>
+                ` : nothing}
            </div>
        </a>`;
                });
@@ -134,19 +148,13 @@ ${content}`, container);
                    const adDescription = ad.node_tag_description;
                    let receiversBlock;
                    if (ad.observers && ad.observers.length >= 1) {
-                        receiversBlock = html`<div class="flex gap-1">
-                            ${ad.observers.map(recv => {
-                                const recvName = recv.tag_name || recv.name || truncateKey(recv.public_key, 12);
-                                return html`<a href="/nodes/${recv.public_key}" class="text-lg hover:opacity-70" title=${recvName}>\u{1F4E1}</a>`;
-                            })}
-                        </div>`;
+                        receiversBlock = html`${observerIcons(ad.observers)}`;
                    } else if (ad.observed_by) {
-                        const recvTitle = ad.observer_tag_name || ad.observer_name || truncateKey(ad.observed_by, 12);
-                        receiversBlock = html`<a href="/nodes/${ad.observed_by}" class="text-lg hover:opacity-70" title=${recvTitle}>\u{1F4E1}</a>`;
+                        receiversBlock = html`<span class="opacity-50">\u{1F4E1}</span>`;
                    } else {
                        receiversBlock = html`<span class="opacity-50">-</span>`;
                    }
-                    return html`<tr class="hover">
+                    return html`<tr class="hover cursor-pointer" @click=${toggleObserverDetail}>
                    <td>
                        <a href="/nodes/${ad.public_key}" class="link link-hover">
                            ${renderNodeDisplay({
@@ -165,7 +173,7 @@ ${content}`, container);
                    </td>
                    <td class="text-sm whitespace-nowrap">${formatDateTime(ad.received_at)}</td>
                    <td>${receiversBlock}</td>
-                </tr>`;
+                </tr>${observerDetailRow(ad.observers || [], null, { hidePath: true })}`;
                });

            const paginationBlock = pagination(page, totalPages, '/advertisements', {
@@ -203,7 +211,7 @@ ${content}`, container);
                <th>${t('entities.node')}</th>
                <th>${t('common.public_key')}</th>
                <th>${t('common.time')}</th>
-                <th>${t('common.receivers')}</th>
+                <th>${t('common.observers')}</th>
            </tr>
        </thead>
        <tbody>
@@ -1,11 +1,12 @@
 import { apiGet } from '../api.js';
 import {
    html, litRender, nothing, t,
-    getConfig, formatDateTime, formatDateTimeShort,
+    getConfig, formatDateTime, formatDateTimeShort, formatRelativeTime,
    getChannelLabelsMap, resolveChannelLabel,
    truncateKey, errorAlert,
    pagination, timezoneIndicator,
-    createFilterHandler, autoSubmit, submitOnEnter
+    createFilterHandler, autoSubmit, submitOnEnter,
+    observerIcons, observerDetailRow, toggleObserverDetail, toggleCardObserverDetail
 } from '../components.js';
 import { createAutoRefresh } from '../auto-refresh.js';

@@ -205,15 +206,9 @@ ${content}`, container);
                        : sender;
                    let receiversBlock = nothing;
                    if (msg.observers && msg.observers.length >= 1) {
-                        receiversBlock = html`<div class="flex gap-0.5">
-                            ${msg.observers.map(recv => {
-                                const recvName = recv.tag_name || recv.name || truncateKey(recv.public_key, 12);
-                                return html`<a href="/nodes/${recv.public_key}" class="text-sm hover:opacity-70" title=${recvName}>\u{1F4E1}</a>`;
-                            })}
-                        </div>`;
+                        receiversBlock = html`<span @click=${toggleCardObserverDetail} class="cursor-pointer">${observerIcons(msg.observers)}</span>`;
                    } else if (msg.observed_by) {
-                        const recvTitle = msg.observer_tag_name || msg.observer_name || truncateKey(msg.observed_by, 12);
-                        receiversBlock = html`<a href="/nodes/${msg.observed_by}" class="text-sm hover:opacity-70" title=${recvTitle}>\u{1F4E1}</a>`;
+                        receiversBlock = html`<span class="opacity-50 text-xs">\u{1F4E1}</span>`;
                    }
                    return html`<div class="card bg-base-100 shadow-sm">
            <div class="card-body p-3">
@@ -236,6 +231,27 @@ ${content}`, container);
                    </div>
                </div>
                <p class="text-sm mt-2 break-words whitespace-pre-wrap">${displayMessage}</p>
+                ${msg.observers && msg.observers.length > 0 ? html`
+                    <div class="observer-detail-card hidden mt-2">
+                        <table class="table table-xs w-full">
+                            <thead><tr><th>Observer</th><th>SNR</th><th>Path</th><th>Received</th></tr></thead>
+                            <tbody>
+                                ${msg.observers.map(o => {
+                                    const dn = o.tag_name || o.name || truncateKey(o.public_key, 12);
+                                    const snrD = o.snr != null ? `${Number(o.snr).toFixed(1)} dB` : '\u2014';
+                                    const pathD = o.path_len != null ? `${o.path_len} hop${o.path_len !== 1 ? 's' : ''}` : '\u2014';
+                                    const timeD = formatRelativeTime(o.observed_at);
+                                    return html`<tr>
+                                        <td>\u{1F4E1} <a href="/nodes/${o.public_key}" class="link link-hover">${dn}</a></td>
+                                        <td>${snrD}</td>
+                                        <td>${pathD}</td>
+                                        <td><span title=${formatDateTime(o.observed_at)}>${timeD}</span></td>
+                                    </tr>`;
+                                })}
+                            </tbody>
+                        </table>
+                    </div>
+                ` : nothing}
            </div>
        </div>`;
                });
@@ -254,19 +270,13 @@ ${content}`, container);
                        : sender;
                    let receiversBlock;
                    if (msg.observers && msg.observers.length >= 1) {
-                        receiversBlock = html`<div class="flex gap-1">
-                            ${msg.observers.map(recv => {
-                                const recvName = recv.tag_name || recv.name || truncateKey(recv.public_key, 12);
-                                return html`<a href="/nodes/${recv.public_key}" class="text-lg hover:opacity-70" title=${recvName}>\u{1F4E1}</a>`;
-                            })}
-                        </div>`;
+                        receiversBlock = html`${observerIcons(msg.observers)}`;
                    } else if (msg.observed_by) {
-                        const recvTitle = msg.observer_tag_name || msg.observer_name || truncateKey(msg.observed_by, 12);
-                        receiversBlock = html`<a href="/nodes/${msg.observed_by}" class="text-lg hover:opacity-70" title=${recvTitle}>\u{1F4E1}</a>`;
+                        receiversBlock = html`<span class="opacity-50">\u{1F4E1}</span>`;
                    } else {
                        receiversBlock = html`<span class="opacity-50">-</span>`;
                    }
-                    return html`<tr class="hover align-top">
+                    return html`<tr class="hover cursor-pointer" @click=${toggleObserverDetail}>
                    <td class="text-lg" title=${typeTitle}>${typeIcon}</td>
                    <td class="text-sm whitespace-nowrap">${formatDateTime(msg.received_at)}</td>
                    <td class="text-sm whitespace-nowrap">
@@ -274,7 +284,7 @@ ${content}`, container);
                    </td>
                    <td class="break-words max-w-md" style="white-space: pre-wrap;">${displayMessage}</td>
                    <td>${receiversBlock}</td>
-                </tr>`;
+                </tr>${observerDetailRow(msg.observers || [])}`;
                });

            const paginationBlock = pagination(page, totalPages, '/messages', {
@@ -326,7 +336,7 @@ ${content}`, container);
                <th>${t('common.time')}</th>
                <th>${t('common.from')}</th>
                <th>${t('entities.message')}</th>
-                <th>${t('common.receivers')}</th>
+                <th>${t('common.observers')}</th>
            </tr>
        </thead>
        <tbody>
@@ -94,7 +94,7 @@
        "public_key": "Public Key",
        "received": "Received",
        "received_by": "Received By",
-        "receivers": "Receivers",
+        "observers": "Observers",
        "from": "From",
        "close": "close",
        "unnamed": "Unnamed",
@@ -118,3 +118,61 @@ class TestListTelemetryFilters:
        assert response.status_code == 200
        data = response.json()
        assert len(data["items"]) == 1
+
+
+class TestTelemetryObservers:
+    """Tests for observer data in telemetry API responses."""
+
+    def test_telemetry_observers_populated(self, client_no_auth, api_db_session):
+        """Test that telemetry list returns observers with data."""
+        from meshcore_hub.common.hash_utils import compute_telemetry_hash
+        from meshcore_hub.common.models import EventObserver, Node, Telemetry
+
+        observer_node = Node(
+            public_key="z" * 64,
+            name="TelObserver",
+            first_seen=datetime.now(timezone.utc),
+        )
+        api_db_session.add(observer_node)
+        api_db_session.flush()
+
+        now = datetime.now(timezone.utc)
+        event_hash = compute_telemetry_hash(
+            node_public_key="tel123tel123tel123tel123tel123tel",
+            parsed_data={"temperature": 22.0},
+            received_at=now,
+        )
+        telemetry = Telemetry(
+            node_public_key="tel123tel123tel123tel123tel123tel",
+            parsed_data={"temperature": 22.0},
+            received_at=now,
+            observer_node_id=observer_node.id,
+            event_hash=event_hash,
+        )
+        api_db_session.add(telemetry)
+        api_db_session.flush()
+
+        ev_obs = EventObserver(
+            event_type="telemetry",
+            event_hash=event_hash,
+            observer_node_id=observer_node.id,
+            snr=8.5,
+            path_len=2,
+            observed_at=now,
+        )
+        api_db_session.add(ev_obs)
+        api_db_session.commit()
+
+        response = client_no_auth.get("/api/v1/telemetry")
+        assert response.status_code == 200
+        data = response.json()
+        items = data["items"]
+        assert len(items) >= 1
+        tel_item = next(
+            i
+            for i in items
+            if i["node_public_key"] == "tel123tel123tel123tel123tel123tel"
+        )
+        assert len(tel_item["observers"]) == 1
+        assert tel_item["observers"][0]["snr"] == 8.5
+        assert tel_item["observers"][0]["path_len"] == 2
@@ -153,3 +153,53 @@ class TestListTracePathsFilters:
        assert response.status_code == 200
        data = response.json()
        assert len(data["items"]) == 1
+
+
+class TestTracePathObservers:
+    """Tests for observer data in trace path API responses."""
+
+    def test_trace_path_observers_populated(self, client_no_auth, api_db_session):
+        """Test that trace path list returns observers with data."""
+        from meshcore_hub.common.hash_utils import compute_trace_hash
+        from meshcore_hub.common.models import EventObserver, Node, TracePath
+
+        observer_node = Node(
+            public_key="z" * 64,
+            name="TraceObserver",
+            first_seen=datetime.now(timezone.utc),
+        )
+        api_db_session.add(observer_node)
+        api_db_session.flush()
+
+        event_hash = compute_trace_hash(initiator_tag=44444)
+        trace = TracePath(
+            initiator_tag=44444,
+            path_hashes=["aa", "bb"],
+            hop_count=2,
+            received_at=datetime.now(timezone.utc),
+            observer_node_id=observer_node.id,
+            event_hash=event_hash,
+        )
+        api_db_session.add(trace)
+        api_db_session.flush()
+
+        ev_obs = EventObserver(
+            event_type="trace",
+            event_hash=event_hash,
+            observer_node_id=observer_node.id,
+            snr=12.0,
+            path_len=3,
+            observed_at=datetime.now(timezone.utc),
+        )
+        api_db_session.add(ev_obs)
+        api_db_session.commit()
+
+        response = client_no_auth.get("/api/v1/trace-paths")
+        assert response.status_code == 200
+        data = response.json()
+        items = data["items"]
+        assert len(items) >= 1
+        trace_item = next(i for i in items if i["initiator_tag"] == 44444)
+        assert len(trace_item["observers"]) == 1
+        assert trace_item["observers"][0]["snr"] == 12.0
+        assert trace_item["observers"][0]["path_len"] == 3
@@ -199,3 +199,20 @@ class TestHandleAdvertisement:
            select(Node).where(Node.public_key == receiver_pk)
        ).scalar_one_or_none()
        assert receiver is not None
+
+    def test_advertisement_stores_snr_and_path_len(self, db_manager, db_session):
+        """Advertisement handler stores snr and path_len in event_observers."""
+        payload = {
+            "public_key": "a" * 64,
+            "name": "TestNode",
+            "adv_type": "chat",
+            "snr": 12.5,
+            "path_len": 3,
+        }
+
+        handle_advertisement("b" * 64, "advertisement", payload, db_manager)
+
+        observer = db_session.execute(select(EventObserver)).scalar_one_or_none()
+        assert observer is not None
+        assert observer.snr == 12.5
+        assert observer.path_len == 3
@@ -18,7 +18,7 @@ class TestHandleContactMessage:
            "pubkey_prefix": "01ab2186c4d5",
            "text": "Hello World!",
            "path_len": 3,
-            "SNR": 15.5,
+            "snr": 15.5,
        }

        handle_contact_message("a" * 64, "contact_msg_recv", payload, db_manager)
@@ -99,7 +99,7 @@ class TestHandleChannelMessage:
            "channel_idx": 4,
            "text": "Channel broadcast",
            "path_len": 10,
-            "SNR": 8.5,
+            "snr": 8.5,
        }

        handle_channel_message("a" * 64, "channel_msg_recv", payload, db_manager)
@@ -158,3 +158,19 @@ class TestHandleChannelMessage:

        msg = db_session.execute(select(Message)).scalar_one()
        assert msg.signature == "abcdef1234567890"
+
+    def test_message_handler_passes_path_len_to_observer(self, db_manager, db_session):
+        """Message handler passes path_len to add_event_observer."""
+        payload = {
+            "pubkey_prefix": "01ab2186c4d5",
+            "text": "Path test",
+            "path_len": 5,
+            "snr": 10.0,
+        }
+
+        handle_contact_message("a" * 64, "contact_msg_recv", payload, db_manager)
+
+        observer = db_session.execute(select(EventObserver)).scalar_one_or_none()
+        assert observer is not None
+        assert observer.path_len == 5
+        assert observer.snr == 10.0
@@ -126,3 +126,18 @@ class TestHandleTelemetry:

        telemetry = db_session.execute(select(Telemetry)).scalar_one()
        assert telemetry.node_public_key == "b" * 64
+
+    def test_telemetry_stores_snr_and_path_len(self, db_manager, db_session):
+        """Telemetry handler stores snr and path_len in event_observers."""
+        payload = {
+            "node_public_key": "b" * 64,
+            "parsed_data": {"temperature": 20.0},
+            "snr": 7.5,
+            "path_len": 2,
+        }
+
+        handle_telemetry("a" * 64, "telemetry_response", payload, db_manager)
+
+        observer = db_session.execute(select(EventObserver)).scalar_one()
+        assert observer.snr == 7.5
+        assert observer.path_len == 2
@@ -88,3 +88,18 @@ class TestHandleTraceData:
        observers = db_session.execute(select(EventObserver)).scalars().all()
        assert len(observers) == 1
        assert observers[0].event_type == "trace"
+
+    def test_trace_stores_snr_and_path_len(self, db_manager, db_session):
+        """Trace handler stores snr and path_len in event_observers."""
+        payload = {
+            "initiator_tag": 88888,
+            "path_len": 4,
+            "snr": 11.5,
+            "hop_count": 2,
+        }
+
+        handle_trace_data("a" * 64, "trace_data", payload, db_manager)
+
+        observer = db_session.execute(select(EventObserver)).scalar_one()
+        assert observer.snr == 11.5
+        assert observer.path_len == 4
@@ -1,4 +1,6 @@
-"""Tests for LetsMesh normalizer _normalize_hash_list method."""
+"""Tests for LetsMesh normalizer."""
+
+from unittest.mock import MagicMock

 from meshcore_hub.collector.letsmesh_normalizer import LetsMeshNormalizer

@@ -66,3 +68,102 @@ class TestNormalizeHashList:
        """Single-character strings are rejected (minimum is 2)."""
        result = LetsMeshNormalizer._normalize_hash_list(["a", "4a"])
        assert result == ["4A"]
+
+
+class TestAdvertisementSnrAndPath:
+    """Tests for SNR and path_len extraction in advertisement payloads."""
+
+    def _make_normalizer(self) -> LetsMeshNormalizer:
+        norm = LetsMeshNormalizer()
+        norm._letsmesh_decoder = MagicMock()
+        norm._include_test_channel = False
+        return norm
+
+    def _make_decoded_type4(self) -> dict:
+        return {
+            "payloadType": 4,
+            "payload": {
+                "decoded": {
+                    "publicKey": "b" * 64,
+                },
+            },
+        }
+
+    def test_advertisement_extracts_snr_from_uppercase_key(self) -> None:
+        """Advertisement payload with uppercase SNR normalizes to lowercase snr."""
+        norm = self._make_normalizer()
+        result = norm._build_letsmesh_advertisement_payload(
+            {"SNR": 12.5, "path": "91CBC3"},
+            decoded_packet=self._make_decoded_type4(),
+        )
+        assert result is not None
+        assert result["snr"] == 12.5
+
+    def test_advertisement_extracts_snr_from_lowercase_key(self) -> None:
+        """Advertisement payload with lowercase snr extracts it."""
+        norm = self._make_normalizer()
+        result = norm._build_letsmesh_advertisement_payload(
+            {"snr": 9.0},
+            decoded_packet=self._make_decoded_type4(),
+        )
+        assert result is not None
+        assert result["snr"] == 9.0
+
+    def test_advertisement_extracts_path_len(self) -> None:
+        """Advertisement payload with path extracts path_len."""
+        norm = self._make_normalizer()
+        result = norm._build_letsmesh_advertisement_payload(
+            {"path": "91CBC3"},
+            decoded_packet=self._make_decoded_type4(),
+        )
+        assert result is not None
+        assert result.get("path_len") is not None
+
+    def test_output_has_lowercase_snr_key_only(self) -> None:
+        """Output contains lowercase snr key, never uppercase SNR."""
+        norm = self._make_normalizer()
+        result = norm._build_letsmesh_advertisement_payload(
+            {"SNR": 8.0},
+            decoded_packet=self._make_decoded_type4(),
+        )
+        assert result is not None
+        assert "snr" in result
+        assert "SNR" not in result
+
+
+class TestMessageSnrCasing:
+    """Tests for message payload SNR casing (lowercase output)."""
+
+    def _make_normalizer(self) -> LetsMeshNormalizer:
+        norm = LetsMeshNormalizer()
+        norm._letsmesh_decoder = MagicMock()
+        norm._include_test_channel = True
+        return norm
+
+    def _make_decoded_type5(self) -> dict:
+        return {
+            "payloadType": 5,
+            "payload": {
+                "decoded": {
+                    "text": "hello channel",
+                    "channel": {"hash": "A" * 24},
+                },
+            },
+        }
+
+    def test_message_outputs_lowercase_snr(self) -> None:
+        """Message payload outputs lowercase snr key, not uppercase SNR."""
+        norm = self._make_normalizer()
+        result = norm._build_letsmesh_message_payload(
+            {
+                "packet_type": "5",
+                "hash": "ABCDEF1234",
+                "SNR": "12.5",
+                "path": "91CBC3",
+            },
+            decoded_packet=self._make_decoded_type5(),
+        )
+        assert result is not None
+        _, payload = result
+        assert "snr" in payload
+        assert "SNR" not in payload
@@ -240,7 +240,7 @@ class TestSubscriber:
        assert payload["text"] == "hello channel"
        assert payload["txt_type"] == 5
        assert "sender_timestamp" not in payload
-        assert payload["SNR"] == 12.5
+        assert payload["snr"] == 12.5
        assert payload["path_len"] == 3

    def test_letsmesh_packet_without_decrypted_text_is_not_shown_as_message(
@@ -1,7 +1,7 @@
 """Tests for database models."""

 import pytest
-from sqlalchemy import create_engine
+from sqlalchemy import create_engine, select
 from sqlalchemy.orm import sessionmaker

 from meshcore_hub.common.models import (
@@ -13,6 +13,8 @@ from meshcore_hub.common.models import (
    TracePath,
    Telemetry,
    EventLog,
+    EventObserver,
+    add_event_observer,
 )


@@ -216,3 +218,45 @@ class TestEventLogModel:
        assert event.event_type == "BATTERY"
        assert event.payload is not None
        assert event.payload["battery_percentage"] == 75
+
+
+class TestEventObserverModel:
+    """Tests for EventObserver model and add_event_observer helper."""
+
+    def test_add_event_observer_stores_path_len(self, db_session) -> None:
+        """add_event_observer accepts and stores path_len."""
+        node = Node(public_key="a" * 64, name="Observer")
+        db_session.add(node)
+        db_session.commit()
+
+        result = add_event_observer(
+            session=db_session,
+            event_type="message",
+            event_hash="abcdef12",
+            observer_node_id=node.id,
+            snr=10.5,
+            path_len=3,
+        )
+        assert result is True
+
+        observer = db_session.execute(select(EventObserver)).scalar_one()
+        assert observer.snr == 10.5
+        assert observer.path_len == 3
+
+    def test_add_event_observer_path_len_defaults_none(self, db_session) -> None:
+        """add_event_observer defaults path_len to None when not provided."""
+        node = Node(public_key="b" * 64, name="Observer2")
+        db_session.add(node)
+        db_session.commit()
+
+        result = add_event_observer(
+            session=db_session,
+            event_type="trace",
+            event_hash="12345678",
+            observer_node_id=node.id,
+        )
+        assert result is True
+
+        observer = db_session.execute(select(EventObserver)).scalar_one()
+        assert observer.path_len is None
+        assert observer.snr is None