Add provider-neutral spec operation

[ferueda]

What changed

• add a provider-neutral Spec operation under lib/spec
• require issue-keyed artifacts at dev/plans/<Linear issue>.md
• align Spec policy with established planning discipline:
  • repository intent and accepted-requirement authority order
  • research and reality reconciliation before structuring
  • resolved planning decisions and explicit executor-time discovery
  • smallest coherent change and vertical delivery slices
  • decision-focused, right-sized, portable artifacts
  • highest stable verification seam
  • focused executor-aid discovery
• validate structured decisions, trusted provenance, and artifact workspace safety
• share normalized work-item schemas between Triage and Spec
• document the new domain and artifact boundaries

Why

FER-273 needs a reusable operation that can research one routed issue and either write a minimum-sufficient implementation Spec or return a true prerequisite question. The operation stays independent of Linear, Inngest, Git, and publication concerns.

The policy keeps the Triage distinction intact: a later reviewer choice does not become Needs Input when the agent can first research options and recommend one, while a missing choice that prevents any coherent scope or architecture stops before an artifact is written.

Impact

This introduces the domain primitive needed by a later thin Inngest Spec consumer. It does not yet route Linear issues, publish plan commits, or change the existing Triage workflow.

Verification

• make check
• focused Spec tests: 59 passed
• change review 20260723-012729-2e3109: implementation and quality passed with zero findings
• docs-drift review completed; both naming/ownership findings fixed in ac169848
• live Codex SDK smoke against Spec policy v2 using gpt-5.6-terra at medium reasoning: 3/3 passed
  • compact change → concise ready-for-review Spec
  • cross-boundary change → coherent reuse of existing persistence and highest CLI/reload test seam
  • unavailable authoritative policy → needs input with no artifact

All live-smoke repositories and logs were disposable and cleaned after the run.

[ferueda]

Summary: The PR adds a Spec operation that writes one issue-keyed plan and documents its domain boundary.

Must-fix drift:

• lib/spec/spec.ts → dev/plans/README.md: distinguish automated Linear Spec artifacts named <ISSUE-KEY>.md from manual planning-workflow files named YYMMDD-short-slug.md; the current “New plans” rule permits only the latter.
• lib/spec/spec.ts → docs/contributing/architecture.md: add the committed issue-keyed Spec artifact to the artifact map and state that the operation writes but does not publish it.

Advisory:

• None.

Verification: make check

[ferueda]

Docs drift triage complete.

Implemented in ac169848:

• dev/plans/README.md now distinguishes manual YYMMDD-short-slug.md plans from Linear Spec <ISSUE-KEY>.md artifacts.
• docs/contributing/architecture.md now records the tracked Spec artifact and keeps publication outside the operation.

No advisory findings remain.

Verification: make check