docs: amend constitution to v1.1.0 (Observability for tracing migration)

Principle V now reflects the merged tracing migration (#148):
- tracing + tracing-opentelemetry spans in every build, with OTLP export
  gated on OTLP_OTLS_ENDPOINT;
- no manual Context threading;
- every spawn / fan-out carries its parent span;
- RUST_LOG gates span export (run at info/debug).
Layer and Tech Stack wording matches.

Also corrects stale "release builds only" telemetry notes in CLAUDE.md and
.env.example, updates the CLAUDE.md dependency list, and fixes the README's
RUST_LOG default. It also documents OTLP_OTLS_ENDPOINT in the README, as
Principle IV requires.

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

.specify/memory/constitution.md

@@ -1,20 +1,31 @@
 <!--
   Sync Impact Report
   ==================
-  Version change: (new) -> 1.0.0
-  Modified principles: N/A (initial ratification)
-  Added sections:
-    - Core Principles (5 principles)
-    - Technology Stack & Constraints
-    - Development Workflow
-    - Governance
+  Version change: 1.0.0 -> 1.1.0
+  Bump rationale: MINOR. Principle V is materially expanded: the tracing
+    mechanism changed (tracing + tracing-opentelemetry in every build), and
+    it adds two new MUST rules: no manual Context threading, and carrying
+    the parent span across spawns. No principle is removed or redefined in
+    intent.
+  Modified principles:
+    - V. Observability: mechanism + rules updated for the tracing migration
+      (map #135, PR #148)
+  Also updated:
+    - I. Layered Architecture: Database Layer "traced" wording
+    - Technology Stack & Constraints: Tracing line
+  Added sections: N/A
   Removed sections: N/A
   Templates requiring updates:
-    - .specify/templates/plan-template.md — ✅ no changes needed (Constitution Check section is generic)
+    - .specify/templates/plan-template.md — ✅ no changes needed (generic Constitution Check)
     - .specify/templates/spec-template.md — ✅ no changes needed
     - .specify/templates/tasks-template.md — ✅ no changes needed
     - .specify/templates/checklist-template.md — ✅ no changes needed
     - .specify/templates/agent-file-template.md — ✅ no changes needed
+  Runtime guidance:
+    - CLAUDE.md "Tracing" — ✅ already consistent (conventions landed with #148);
+      OTLP env line + dependency list updated alongside this amendment
+    - README.md — ✅ RUST_LOG default/gating corrected; OTLP_OTLS_ENDPOINT added
+    - .env.example — ✅ telemetry header corrected
   Follow-up TODOs: None
 -->
 
@@ -34,7 +45,8 @@ All features MUST follow the established layered architecture:
   contracts. Every DAO MUST be defined as a trait to enable mock
   implementations for testing.
 - **Database Layer** (Diesel ORM, `schema.rs`): Concrete `Sqlite*Dao`
-  implementations. All queries traced with OpenTelemetry.
+  implementations. Every query runs inside a `tracing` span via
+  `otel::trace_db_call`.
 
 New features MUST NOT bypass layers (e.g., HTTP handlers MUST NOT
 execute raw SQL). Actix actors are permitted for long-running async
@@ -84,17 +96,35 @@ prohibited.
 
 ### V. Observability
 
-All database operations and HTTP handlers MUST be instrumented
-with OpenTelemetry spans via the `trace_db_call` helper or
-equivalent tracing macros.
+All database operations and HTTP handlers MUST be instrumented with
+`tracing` spans, exported through `tracing-opentelemetry`: DAO bodies via
+`otel::trace_db_call`, and handlers / feature functions via
+`#[tracing::instrument]`. The per-request root span comes from the
+`tracing-actix-web` middleware, which also honors an incoming W3C
+`traceparent`.
 
-- Release builds export traces to the configured OTLP endpoint.
-- Debug builds use the basic logger.
+- Spans are produced in debug and release builds alike. OTLP export is
+  enabled by `OTLP_OTLS_ENDPOINT`, not by build profile.
+- Code MUST NOT thread an OpenTelemetry `Context` through call chains.
+  Spans parent on the ambient span.
+- Every `tokio::spawn` or cross-thread fan-out (rayon, per-pass runtimes)
+  MUST carry its parent span: `.instrument(span)` or
+  `info_span!(parent: &span, ...)`. Tracing context is thread-local, and
+  an uncarried spawn orphans its spans onto a fresh trace.
+- `RUST_LOG` gates span export as well as console output (one `EnvFilter`).
+  Deployments MUST run at `info` or `debug`.
+- Logs are a separate pipeline: `env_logger` in debug, OTel log export in
+  release.
 - Prometheus metrics (`imageserver_image_total`,
   `imageserver_video_total`) MUST be maintained for key counters.
 - Errors MUST be logged at `error!` level with sufficient context
   for debugging without reproducing the issue.
 
+**Rationale:** span parenting that relies on hand-threaded contexts drifted
+into orphaned traces (the pre-migration baseline, #137). Ambient
+parenting, plus an explicit carry at each spawn boundary, keeps a request or
+job in one trace by construction.
+
 ## Technology Stack & Constraints
 
 - **Language**: Rust (stable toolchain, Cargo build system)
@@ -105,8 +135,9 @@ equivalent tracing macros.
 - **Video Processing**: ffmpeg/ffprobe (CLI, must be on PATH)
 - **Image Processing**: `image` crate for thumbnails, `kamadak-exif`
   for EXIF extraction
-- **Tracing**: OpenTelemetry with OTLP export (release),
-  basic logger (debug)
+- **Tracing**: `tracing` + `tracing-opentelemetry` (every build), OTLP
+  export when `OTLP_OTLS_ENDPOINT` is set; logs via `env_logger` (debug) /
+  OTel log export (release)
 - **Testing**: `cargo test`, `actix_web::test`, in-memory SQLite
 
 External dependencies (ffmpeg, Ollama) are optional runtime
@@ -146,4 +177,4 @@ MUST comply with these principles.
   these principles. The CLAUDE.md file provides runtime development
   guidance and MUST remain consistent with this constitution.
 
-**Version**: 1.0.0 | **Ratified**: 2026-02-26 | **Last Amended**: 2026-02-26
+**Version**: 1.1.0 | **Ratified**: 2026-02-26 | **Last Amended**: 2026-09-29