Task: Integrate first conversation latency fix

Identity

Merge source commit 08da976 into the latest clean main baseline a7340a2 through this isolated integration branch.
Preserve the first-send known-empty session fast path, the narrow upstream-saturation terminal projection, and their focused unit/Electron E2E coverage.
Promote the durable session-cache and Host AI proxy contracts into canonical project memory, then advance main only after verification and independent review.

Treat source task 20260812-first-chat-fix-b84fd29c as read-only evidence; do not rewrite its record during integration.
Preserve the existing Renderer -> Host API -> Electron Main -> OpenCode ownership boundary and generic 429 behavior.
Do not claim that every source of cold-start latency is eliminated: this integration removes the redundant known-empty history wait and stops indefinite retries only for explicitly classified upstream saturation.
Preserve main commit a7340a2 and all unrelated in-flight task work; no remote push is authorized by this task.
Revalidate the status projection whenever the bundled OpenCode retry contract changes.

.project-docs/05-agent-entry/memory-index.md
.project-docs/30-worklog/current-state.md
.project-docs/00-brief/project-positioning.md
.project-docs/10-decisions/decision-index.md
.project-docs/20-architecture/system-overview.md
.project-docs/20-architecture/module-map.md
.project-docs/20-architecture/data-flow.md
.project-docs/40-domain/business-rules.md
.project-docs/00-brief/success-criteria.md
.project-docs/50-evidence/evidence-index.md
.project-docs/60-reflection/reflection-index.md
.project-docs/80-commitments/commitments.md
.project-docs/90-maintenance/stale-items.md
.project-docs/05-agent-entry/integration-gate.md
Source task record 20260812-first-chat-fix-b84fd29c
Active peer task Scope / Intent And Constraints / Promotion Candidates sections required by the planning gate.

Merge 08da976 without rewriting source history and inspect the combined diff against a7340a2.
Record the durable OpenCode session-cache and Host AI proxy contracts in canonical memory.
Run focused unit tests, typecheck, scoped lint, Vite build, Electron E2E, full-suite baseline comparison, and documentation checks.
Obtain an independent read-only PASS/FAIL review, complete integration documentation, and fast-forward main through a clean promotion task.

Merged source commit 08da976 into the latest main baseline with integration merge 0ee5254, preserving both parents while keeping the source task record read-only on its source branch.
Integrated the known-empty session fast path: first prompt submission no longer waits for a redundant empty-history request, while unknown and ordinary historical sessions retain defensive loading/refresh behavior.
Integrated the narrow Host AI proxy saturation projection: quota exhaustion remains 402, explicit upstream-group saturation becomes terminal 400 for bundled OpenCode 1.18.9, and generic rate limits remain 429.
Promoted the session-cache own-key contract, proxy retry boundary, verification evidence, and OpenCode-upgrade revalidation commitment into canonical project memory.

Focused unit tests: 4 files / 228 tests passed.
pnpm run typecheck: passed.
ESLint over all changed product, unit, and Electron E2E files: passed.
pnpm run build:vite: passed for Renderer, Electron Main, and Preload.
pnpm exec playwright test tests/e2e/opencode-first-chat.spec.ts: passed, 1/1 in 4.7 seconds on the stable build output. An earlier attempt ran concurrently with build:vite and timed out during Electron launch before test logic; the serial rerun passed.
pnpm test: 1548/1551 tests passed. The same three failures were independently reproduced on pre-integration main: two timing/generation cases in opencode-manager.test.ts and the missing repository .opencode/agent fixture in youth-plain-language-skill.test.ts.
check_project_docs.py: passed.
check_doc_drift.py --task-id 20260812-integrate-first-chat-fix-c31e: passed after the integration merge was amended so the source task record remains only in source history.
git diff --check: passed with only the repository's normal LF/CRLF checkout warnings.
Independent final read-only Sol review: PASS with no blocking findings; it independently reran all 228 related unit tests and confirmed merge ancestry, source-tree equality, cache/error semantics, and canonical documentation accuracy.

Revalidate or remove the internal saturation status projection when bundled OpenCode or the upstream error contract changes.
Treat duplicate cold bootstrap work and coarse global loading state as separate optimization candidates; this integration does not claim that all runtime cold-start latency is eliminated.