fix(routing): repair pass-rate instrumentation (3 bugs) — #73, #35

The #35 data gate could never fill: a real review call routed cleanly to
qwen36 but /pass-rate stayed total:0 under every key. Root cause was three
independent defects in the session_log path, each alone fatal:

- A: a successful routed call logged final_status "skip", never "pass".
  /pass-rate computes pass/(pass+fail) and skips count as neither, so the
  >=0.90 gate was mathematically unreachable. Success now logs "pass".
- B: every record was written under skill "_routing", so /pass-rate?skill=
  review|debug (what #35 measures) always read zero. Now uses the real
  e.Skill; routing decisions stay groupable via session_id "_routing".
- C: the session_log POST to the bearer-gated ingestion /mcp carried no
  Authorization header → silent 401, swallowed by best-effort logging
  (the documented mcpclient-empty-token-silent-401 footgun). Logger now
  takes a token (BRAIN_MCP_TOKEN) and sets the bearer when non-empty.

Tests rewritten to assert correct behavior (they had encoded the bugs:
"skip" on success, "_routing" skill). New test covers the auth header and
the empty-token path.

Infra (BRAIN_MCP_TOKEN ExternalSecret + env on the routing deployment) and
redeploy follow separately. Refs #73, #35.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/routing/log.go

@@ -17,19 +17,24 @@ type LogEntry struct {
 	Message     string // free-form, e.g. "model=qwen35, pass_rate=0.94"
 	ProjectRoot string
 	DurationMs  int64
-	Failed      bool // true → final_status: "fail"; false → "skip"
+	Failed      bool // true → final_status: "fail"; false → "pass"
 }
 
 // Logger posts session_log entries to a brain MCP at BrainURL + /mcp.
 type Logger struct {
 	BrainURL string
+	Token    string // bearer for the (auth-gated) ingestion /mcp; empty = no header
 	HTTP     *http.Client
 }
 
-// NewLogger creates a Logger with a 2-second HTTP timeout.
-func NewLogger(brainURL string) *Logger {
+// NewLogger creates a Logger with a 2-second HTTP timeout. token authenticates
+// to the bearer-gated ingestion /mcp; an empty token sends no Authorization
+// header (and silently 401s against a gated server — see brain
+// mcpclient-empty-token-silent-401-envfrom-missing-key).
+func NewLogger(brainURL, token string) *Logger {
 	return &Logger{
 		BrainURL: brainURL,
+		Token:    token,
 		HTTP:     &http.Client{Timeout: 2 * time.Second},
 	}
 }
@@ -37,7 +42,10 @@ func NewLogger(brainURL string) *Logger {
 // LogDecision posts a session_log MCP call. Errors are returned but the caller
 // MUST NOT block real work on them — logging is best-effort.
 func (l *Logger) LogDecision(ctx context.Context, e LogEntry) error {
-	status := "skip"
+	// A completed routed call is a pass (liveness); only an execution error is a
+	// fail. There is no "skip" for routing — the prior default-to-"skip" meant a
+	// successful call never counted toward pass_rate, so the gate was unreachable.
+	status := "pass"
 	if e.Failed {
 		status = "fail"
 	}
@@ -48,8 +56,10 @@ func (l *Logger) LogDecision(ctx context.Context, e LogEntry) error {
 		"params": map[string]any{
 			"name": "session_log",
 			"arguments": map[string]any{
-				"session_id":   e.SessionID,
-				"skill":        "_routing",
+				"session_id": e.SessionID,
+				// The real skill, so /pass-rate?skill=review|debug sees these
+				// records; routing decisions stay groupable via session_id "_routing".
+				"skill":        e.Skill,
 				"phase":        "decide",
 				"final_status": status,
 				"message":      fmt.Sprintf("%s: %s — %s", e.Skill, e.Decision, e.Message),
@@ -67,6 +77,9 @@ func (l *Logger) LogDecision(ctx context.Context, e LogEntry) error {
 		return fmt.Errorf("log: build request: %w", err)
 	}
 	req.Header.Set("Content-Type", "application/json")
+	if l.Token != "" {
+		req.Header.Set("Authorization", "Bearer "+l.Token)
+	}
 	resp, err := l.HTTP.Do(req)
 	if err != nil {
 		return fmt.Errorf("log: request: %w", err)