feat(garmin): all-JSON wrapper protocol and log stream

Error responses from wrapper.py now carry error_type and traceback in
the protocol itself, logged as attrs on the Go side's per-call record.
wrapper.py's free-text stderr debug prints become JSON log lines
({level,msg,...attrs}); client.go parses that stream and re-emits it
through the application logger (level-mapped, source=garmin-wrapper),
wrapping any non-JSON line instead of passing it through raw. The
wrapper also survives malformed request lines and unserializable
results with JSON responses instead of crashing with a raw traceback.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.claude/skills/geniusrun-dev/SKILL.md

@@ -58,7 +58,7 @@ Each `workout_kinds.rule_json` is a recursive AND/OR condition tree (`internal/c
 `internal/garmin` spawns a small Python wrapper script (`internal/garmin/pyscript/wrapper.py`, embedded into the Go binary via `go:embed`) that imports `garminconnect` directly and speaks a minimal newline-delimited-JSON protocol over stdin/stdout: `{"id","cmd","params"}` in, `{"id","result"}` or `{"id","error"}` out. `cmd` is `authenticate`, `complete_mfa`, or a fully generic `call` (`{"method": "<any garminconnect.Garmin method>", "args": {...}}`) — there's no MCP layer, and the separate `mcp-garmin` repo this used to depend on is retired. Key things learned the hard way, that would otherwise get rediscovered:
 
 - **`authenticate`/`complete_mfa` return structured JSON** (`{"status": "success"|"mfa_required"|"failed", "message": "..."}`), not plain strings — `internal/garmin/client.go` maps `status` directly to `AuthStatus`, no string pattern-matching.
-- **The 10s "MFA required" timeout in `wrapper.py`'s `authenticate` handler is a false-positive trap.** A login that's merely slow (e.g. Garmin/Cloudflare rate-limiting) looks identical to a real MFA challenge unless you check whether `prompt_mfa()` was actually invoked (`wrapper.py` logs this to stderr for exactly this reason).
+- **The 10s "MFA required" timeout in `wrapper.py`'s `authenticate` handler is a false-positive trap.** A login that's merely slow (e.g. Garmin/Cloudflare rate-limiting) looks identical to a real MFA challenge unless you check whether `prompt_mfa()` was actually invoked (`wrapper.py` emits a JSON log line for exactly this reason, forwarded into the Go log stream by `forwardWrapperStderr`).
 - **`wrapper.py` persists Garmin sessions** via a `GARMIN_TOKENSTORE` env var (the Go→Python subprocess protocol variable — the process-level config var is `GENIUSRUN_TOKENSTORE_PATH`) passed to `Garmin.login(tokenstore=...)` — without this, every process start does a full SSO login, which is what trips Garmin's rate limiting under repeated testing.
 - **`activityId` is a large int64** — never round-trip it through `float64`/generic `map[string]any` JSON decoding, or it corrupts into scientific notation. Decode into typed structs (`garmin.Activity`, not `map[string]any`).
 - **`get_activity_details` returns raw per-second telemetry** (`activityDetailMetrics` + `metricDescriptors`), not lap/split summaries. Its `metricDescriptors` index-to-field mapping is **not stable across activities/devices** — `garmin.ExtractSamples` always resolves fields by descriptor key, never by fixed array position.