feat(trigger-service): classifier + start/resume matchers (TS-IMPL-012)

[toddysm]

TS-IMPL-012 — Classifier + Start Matcher + Resume Matcher

Implements the Classify → Match stage of the trigger pipeline (issue #642,
design § Module responsibilities).

What

• pipeline/classify.py — classify(event) -> Classification(to_start, to_resume).
  Every event is a start candidate; every event except a manual fire
  (source.type == manual, a direct targeted start trigger) is also a resume
  candidate. Both arms can match the same event.
• pipeline/match_start.py — StartMatcher.match(event, candidates) keeps the
  active kind=start subscriptions whose CEL selector evaluates True (no
  selector = unconditional; a non-bool result is a no-match per design
  § Selector Language).
• pipeline/match_resume.py — ResumeMatcher.match(event, candidates) resumes
  kind=resume subscriptions on an exact (runId, stepId, eventKey) triple,
  then narrows by the optional CEL selector. resume_key_from_event reads
  runId/stepId from event.data and uses event.kind as the event key; an
  event with no run context yields no resume matches.

Design note

The matchers are pure routing functions over a caller-supplied candidate set.
The locked SPL MetadataStoreProvider exposes no subscription/resume list
surface (only the write methods + the dev/test in-memory read accessors), so
candidate enumeration is the receiver/dispatcher's concern (TS-IMPL-014..018) —
the matchers focus on the selection logic the scope describes.

Acceptance

• An event can match both arms; resume match is exact on the triple. ✅
• Start matches gated by the CEL selector. ✅
• classify.py / match_start.py / match_resume.py at 100% coverage;
  suite 321 passed. ✅
• ruff + mypy clean. ✅

Closes #642

[Copilot]

Pull request overview

Implements the Trigger Service pipeline’s Classify → Match stage (TS-IMPL-012), adding pure routing/matching helpers that operate over a caller-supplied candidate set and are gated by CEL selector evaluation.

Changes:

• Added classify(event) -> Classification to route every event to the start arm and route all non-manual events to the resume arm.
• Added StartMatcher (active kind=start + optional CEL selector) and ResumeMatcher (exact (runId, stepId, eventKey) + optional CEL selector), plus resume_key_from_event.
• Added unit tests covering classifier behavior and matcher semantics (including non-bool selector results as no-match) and marked TS-IMPL-012 as complete in the design TODOs.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/services/trigger-service/src/custos_trigger/pipeline/classify.py	Adds classifier that routes events to start and (usually) resume arms.
src/services/trigger-service/src/custos_trigger/pipeline/match_start.py	Adds start-subscription matcher (active start + CEL selector gating).
src/services/trigger-service/src/custos_trigger/pipeline/match_resume.py	Adds resume matcher with exact triple matching + optional CEL selector narrowing.
src/services/trigger-service/src/custos_trigger/pipeline/init.py	Exposes the pipeline surface area via package exports.
src/services/trigger-service/tests/test_pipeline.py	Adds focused unit coverage for classifier, matchers, and resume key extraction.
design/components/trigger-service/todos.md	Updates TS-IMPL-012 status to completed.

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