Docs: RUST_LOG also gates span export (#135)

The subscriber's single EnvFilter fronts both the console and the OTel
layer, so RUST_LOG decides which spans exist for export. Documented in
CLAUDE.md (supported range info/debug) and at the filter in init_tracing.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -581,6 +581,16 @@ an incoming `traceparent`). Conventions:
   never hold `span.enter()` across an `.await`.
 - DB: `otel::trace_db_call`; LLM: `otel::start_llm_request_span` (injects
   `traceparent` downstream).
+- **`RUST_LOG` gates spans, not just logs.** The subscriber's single
+  `EnvFilter` sits in front of both the console and the OTel layer, so a span
+  below the filter level is never created: it's missing from the export, it
+  breaks the parent chain for its children, and an `llm.request` below it
+  sends no `traceparent`. Every span in the codebase is `info` level, so
+  `RUST_LOG=info` or `debug` (the supported range) exports everything;
+  `warn`/`error` silently turns tracing off. Per-target overrides like
+  `RUST_LOG=info,image_api::otel=warn` drop just those spans (here: DB and
+  LLM). If export ever needs to be independent of console verbosity, give
+  the OTel layer its own per-layer filter in `otel::init_tracing`.
 
 **Memory Exclusion:**
 `PathExcluder` in `memories.rs` filters out directories from memories API via `EXCLUDED_DIRS` environment variable (comma-separated paths or substring patterns). The same excluder is applied to face-detection candidates (`face_watch::filter_excluded`) so junk directories like `@eaDir` / `.thumbnails` don't burn detect calls on Apollo.
@@ -665,7 +675,7 @@ GIFS_DIRECTORY=/path/to/gifs           # Video GIF thumbnails
 BIND_URL=0.0.0.0:8080                  # Server binding
 CORS_ALLOWED_ORIGINS=http://localhost:3000
 SECRET_KEY=your-secret-key-here        # JWT signing secret
-RUST_LOG=info                          # Log level
+RUST_LOG=info                          # Log level; also gates span export (keep at info/debug, see "Tracing")
 EXCLUDED_DIRS=/private,/archive        # Comma-separated paths to exclude from memories
 ```