Add call graph fixtures for various languages and scenarios

- Introduced `all-edge-reasons.json` to test edge resolution reasons in .NET.
- Added `all-visibility-levels.json` to validate method visibility levels in .NET.
- Created `dotnet-aspnetcore-minimal.json` for a minimal ASP.NET Core application.
- Included `go-gin-api.json` for a Go Gin API application structure.
- Added `java-spring-boot.json` for the Spring PetClinic application in Java.
- Introduced `legacy-no-schema.json` for legacy application structure without schema.
- Created `node-express-api.json` for an Express.js API application structure.

docs/api/orchestrator-first-signal.md

@@ -0,0 +1,102 @@
+# Orchestrator · First Signal API
+
+Provides a fast “first meaningful signal” for a run (TTFS), with caching and ETag-based conditional requests.
+
+## Endpoint
+
+`GET /api/v1/orchestrator/runs/{runId}/first-signal`
+
+### Required headers
+- `X-Tenant-Id`: tenant identifier (string)
+
+### Optional headers
+- `If-None-Match`: weak ETag from a previous 200 response (supports multiple values)
+
+## Responses
+
+### 200 OK
+Returns the first signal payload and a weak ETag.
+
+Response headers:
+- `ETag`: weak ETag (for `If-None-Match`)
+- `Cache-Control: private, max-age=60`
+- `Cache-Status: hit|miss`
+- `X-FirstSignal-Source: snapshot|cold_start` (best-effort diagnostics)
+
+Body (`application/json`):
+```json
+{
+  "runId": "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa",
+  "firstSignal": {
+    "type": "started",
+    "stage": "unknown",
+    "step": null,
+    "message": "Run started",
+    "at": "2025-12-15T12:00:10+00:00",
+    "artifact": { "kind": "run", "range": null }
+  },
+  "summaryEtag": "W/\"...\""
+}
+```
+
+### 204 No Content
+Run exists but no signal is available yet (e.g., run has no jobs).
+
+### 304 Not Modified
+Returned when `If-None-Match` matches the current ETag.
+
+### 404 Not Found
+Run does not exist for the resolved tenant.
+
+### 400 Bad Request
+Missing/invalid tenant header or invalid parameters.
+
+## ETag semantics
+- Weak ETags are computed from a deterministic, canonical hash of the stable signal content.
+- Per-request diagnostics (e.g., cache hit/miss) are intentionally excluded from the ETag material.
+
+## Streaming (SSE)
+The run stream emits `first_signal` events when the signal changes:
+
+`GET /api/v1/orchestrator/stream/runs/{runId}`
+
+Event type:
+- `first_signal`
+
+Payload shape:
+```json
+{
+  "runId": "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa",
+  "etag": "W/\"...\"",
+  "signal": { "version": "1.0", "signalId": "...", "jobId": "...", "timestamp": "...", "kind": 1, "phase": 6, "scope": { "type": "run", "id": "..." }, "summary": "...", "etaSeconds": null, "lastKnownOutcome": null, "nextActions": null, "diagnostics": { "cacheHit": false, "source": "cold_start", "correlationId": "" } }
+}
+```
+
+## Configuration
+
+`appsettings.json`:
+```json
+{
+  "FirstSignal": {
+    "Cache": {
+      "Backend": "inmemory",
+      "TtlSeconds": 86400,
+      "SlidingExpiration": true,
+      "KeyPrefix": "orchestrator:first_signal:"
+    },
+    "ColdPath": {
+      "TimeoutMs": 3000
+    },
+    "SnapshotWriter": {
+      "Enabled": false,
+      "TenantId": null,
+      "PollIntervalSeconds": 10,
+      "MaxRunsPerTick": 50,
+      "LookbackMinutes": 60
+    }
+  },
+  "messaging": {
+    "transport": "inmemory"
+  }
+}
+```