[plan-12] Provider & Extensibility Roadmap — net-new capabilities, not defects

Defect

This is a roadmap master, not a defect cluster: it aggregates net-new capabilities across providers, ingestion/filtering, observability, auth, and UX so they ship as coherent slices rather than one-off PRs.

Children

Providers & auth

• #2522 — Vertex AI support for the Gemini provider (GCP service-account / ADC + Vertex endpoint)
• #2704 — auth-helper command for refreshable gateway tokens (apiKeyHelper equivalent)

Ingestion & filtering

• #2690 — backfill / ingest existing Claude Code session JSONL files
• #2498 — incremental scan skill for changes made outside a Claude session
• #2463 — tool_response-level filter (extension / size / content heuristic) to prevent binary/Playwright blowups
• #2423 — per-directory disable support
• #2711 — option to write worktree observations to the parent project
• #2736 — skip / throttle subagent observations (Dynamic Workflow workflow-subagent) — re-raise of #2303

Observability & logging

• #2566 — MCP grammar-introspection routes + worker provider retry telemetry + audit log
• #2513 — clarify logger audit policy and codify CI behavior
• #2702 — logging cleanup: type-safe Component union, dead-log removal, noise reduction

UX / semantics / extensibility

• #2645 — i18n support for startup UI labels
• #2467 — PreToolUse:Read injection treated as a turn boundary in connected tool sequences (semantics call)
• #2418 — enable OpenHarness integration / allow PR from fork

Fix sequence

Design doc: plans/12-provider-and-extensibility-roadmap.md. Ship per sub-area as independent slices; each slice carries its own tests. No single PR closes this master — it closes when its sub-areas land.

Out of scope

All defect clusters (plan-01..11, plan-13).