Agent host: consolidate Claude SDK query build (Tier 0 + C1)

[TylerLeonhardt]

What

First step of a planned consolidation of the Claude agent-host runtime (full plan in src/vs/platform/agentHost/node/claude/architecture-analysis/ROADMAP.md). Two low-risk, self-contained changes:

Tier 0 — remove dead code (grep-confirmed zero production callers):

• ClaudeAgentSession.{seedBijectiveState, attachRematerializer, rebindForClientTools}
• ClaudeSdkPipeline.{setClientToolOwner, reloadPlugins}
• ClaudeSdkMessageRouter.setClientToolOwner

C1 — unify the SDK-Options build. The two near-identical buildOptions sites (initial materialize + the rematerializer closure, ~50% copy-paste) collapse into one ClaudeAgentSession._startSdkQuery, with a thin _rebuildSdkQuery wrapper. The pipeline's rebuild hook moves from a post-construction attachRematerializer to a required constructor param — removing the two-phase init and the throw-if-unattached. The closure-captured ctx becomes an explicit _sdkStart field (de-closured). Net: buildOptions has a single caller; model/effort no longer derived a third time; −85 lines.

Why

Reduces the "rematerializer" duplication + two-phase-init smell without changing behavior. It's the enabling step for the bigger reshape — C9: immutable pipeline / session-orchestrated rebind (stacked next) — that removes the passed-in rematerializer entirely. The architecture-analysis/ dir has the coupling/lifecycle/duplication analysis, a synthesis with diagrams, and the sequenced roadmap.

Validation

• typecheck-client + eslint clean; 213 unit tests pass.
• Adversarial review (4 finder angles: line-by-line, removed-behavior, cross-file, cleanup): no correctness bugs; 2 cleanups applied (_clientToolOwner → readonly; reuse resolveCurrentPermissionMode).
• Live E2E in the authenticated Agents window: materialize (startup isResume=false), pipeline reuse (1 startup / 4 turns), abort→cancellation, and recover-rebind (startup isResume=true → result) all confirmed end-to-end; no "no rematerializer attached" errors.

Not in this PR

• C9 (immutable pipeline) — stacked on top; C2 folds into it.
• Config-state model recorded in CONTEXT.md M5 (Desired-on-session / Applied-on-pipeline; per-axis timing).

Review note

Draft — opened early for directional feedback ahead of the stacked C9 PR. The architecture-analysis/ docs are working notes/analysis (candid by design); happy to trim if reviewers prefer a leaner tree.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Consolidates Claude SDK query construction and removes unused APIs.

Changes:

• Centralizes initial and rebuilt SDK query startup.
• Requires rematerialization during pipeline construction.
• Updates tests and adds architecture planning documentation.

Show a summary per file

File	Description
claudeSdkPipeline.test.ts	Updates rematerializer test wiring.
claudeAgent.test.ts	Corrects state-seeding terminology.
CONTEXT.md	Documents config ownership and timing.
claudeSdkPipeline.ts	Requires rebuild callback; removes dead APIs.
claudeSdkMessageRouter.ts	Makes tool-owner resolver immutable.
claudeAgentSession.ts	Centralizes SDK query startup and rebuilding.
architecture-analysis/ROADMAP.md	Defines the consolidation roadmap.
architecture-analysis/README.md	Indexes architecture reports.
architecture-analysis/C1-e2e-scenarios.md	Documents C1 validation scenarios.
architecture-analysis/05-test-surface.md	Analyzes testability.
architecture-analysis/04-responsibility-overlap.md	Analyzes responsibility boundaries.
architecture-analysis/03-rematerializer-and-duplication.md	Analyzes query-build duplication.
architecture-analysis/02-lifecycle-and-ownership.md	Audits lifecycle ownership.
architecture-analysis/01-call-graph-and-closures.md	Maps dependencies and callbacks.
architecture-analysis/00-SYNTHESIS.md	Synthesizes architecture findings.

Review details

• Files reviewed: 15/15 changed files
• Comments generated: 6
• Review effort level: Medium

[TylerLeonhardt]

Thanks — all 6 addressed in 1950d05:

1. CONTEXT.md M5 (config-state) — relabeled as the C9 target state and documented the interim _currentModel / _currentEffort / _currentPermissionMode cache the pipeline still holds today, so it no longer contradicts the runtime.
2. architecture-analysis/README.md — roadmap range updated to C1–C9.
3. _sdkStart JSDoc — trimmed to one line (the field type conveys the rest).
4. _startSdkQuery JSDoc — reduced to the contract.
5. _rebuildSdkQuery JSDoc — reduced to the contract.
6. claudeSdkPipeline.test.ts harness comment — condensed to one line.