fix(opencode): switch session models without restart

.project-docs/30-worklog/tasks/20260820-session-model-agent-hotfix-6e4c9a2f.md

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+# Task: Implement session model parity and partner hot reload
+
+## Identity
+
+- Task ID: 20260820-session-model-agent-hotfix-6e4c9a2f
+- Mode: Feature
+- Branch: codex/20260820-session-model-agent-hotfix-6e4c9a2f-session-model-agent-hotfix
+- Worktree: D:\Datas\OthersProjects\makelore-session-model-agent-hotfix-6e4c9a2f
+- Base commit: 1c6b00443631ad41929e79943bbea9bc7126b563
+- Owner: codex
+- Status: Ready for Integration
+
+## Scope
+
+- Make the AI programming chat model selector and `/models` / `/model` commands switch the active OpenCode Session model through OpenCode's native session API.
+- Preserve the Session-selected model across later prompts, project commands, compaction, Session switching, and Session-list hydration without rewriting partner or Provider configuration.
+- Allow a newly created unique-id project Agent to execute in the current fresh runtime generation once the live Agent registry exposes that id.
+- Keep same-id Agent edits, deletion/recreation, attached or unknown runtime generations, and missing live ids fail-closed until a fresh generation rollover.
+- Add focused unit and Electron E2E coverage and synchronize README product behavior.
+
+## Intent And Constraints
+
+- Page model switching must have the same OpenCode Session semantics as the runtime model command and must not trigger runtime restart, reload, dispose, or Provider persistence.
+- Partner `model` remains the default for a new Session; the active model of an existing Session is owned by OpenCode.
+- Ordinary prompts and project commands must not resend a model override that would undo a Session switch.
+- A live same-id registry entry is not evidence that edited content was reloaded. Hot acceptance is restricted to an id never seen in the current generation; removed ids remain known and cannot be recreated hot.
+- Preserve manager-to-project lock ordering, bounded runtime acceptance, attached/unknown fail-closed behavior, and all existing project Agent prompt/template structures.
+- Work remained isolated in the claimed feature worktree; canonical `.project-docs` files were not modified.
+
+## Outcome
+
+- Added an OpenCode client adapter for `POST /api/session/{sessionID}/model`, a Main-owned Host API route, and Renderer Store state/action for per-Session model switching.
+- Replaced the read-only composer model label with a Session selector. The selector and `/models` / `/model` share one action; successful switches update only Session state and can be hydrated from OpenCode Session metadata.
+- Removed automatic model overrides from ordinary prompt and project-command submissions. Compaction and attachment capability projection now use the active Session model.
+- Changed project Agent readiness from a whole-manifest execution gate to per-Agent desired/applied tracking. Existing unchanged Agents remain usable when a peer is added, and a new unique id becomes usable only after it appears in the live registry.
+- Preserved sticky pending behavior for same-id edits, missing live Agents, attached/unknown generations, and delete/recreate of an id. A new fresh runtime generation remains the authoritative reset.
+- Updated README and the multi-chat Electron E2E fixture to document and exercise Session switching without prompt model overwrite.
+
+## Verification
+
+- `corepack pnpm run typecheck` — passed.
+- `corepack pnpm run lint:check` — passed with 0 errors and 6 pre-existing warnings in unrelated files.
+- Focused unit suite for Agent runtime, routes, client, Store, command registry/hook, and ChatPanel — 405 tests passed.
+- `corepack pnpm test` — 176 files, 2068 tests passed.
+- `corepack pnpm run build:vite` — passed; only existing chunk-size/dynamic-import warnings were reported.
+- `corepack pnpm run test:e2e -- tests/e2e/opencode-multichat-runtime.spec.ts` — 1 Electron E2E passed.
+- `git diff --check` — passed; only configured LF-to-CRLF notices were emitted.
+
+## Follow-ups
+
+- Integration should reconcile the canonical OpenCode Agent readiness and Session model ownership descriptions listed below.
+
+## Promotion Candidates
+
+### Per-Agent runtime acceptance
+
+- Target canonical documents: `.project-docs/20-architecture/module-map.md` and `.project-docs/20-architecture/data-flow.md`.
+- Proposal: replace the whole-manifest-only Agent readiness description with per-Agent desired/applied state. A unique id first seen in an owned fresh generation may be accepted after live registry discovery; same-id edits and delete/recreate remain pending until generation rollover.
+- Evidence: `electron/opencode/project-agent-runtime.ts`, `tests/unit/project-agent-runtime.test.ts`, and the Agent readiness cases in `tests/unit/opencode-routes.test.ts`.
+- Future impact: future Agent configuration work must preserve the distinction between identity discovery and same-id content reload, and must not restore a whole-manifest gate that blocks existing Agents when adding a peer.
+- Semantic conflicts: canonical docs currently describe a whole desired/applied fingerprint and state that live id alone cannot prove content. The proposal refines this by using first-seen unique identity as the safe hot-add boundary while retaining the same-id restriction.
+- Human confirmation required: no; this behavior was explicitly requested and is covered by regression tests.
+
+### OpenCode Session model ownership
+
+- Target canonical documents: `.project-docs/20-architecture/module-map.md`, `.project-docs/20-architecture/data-flow.md`, and `.project-docs/40-domain/business-rules.md`.
+- Proposal: document partner model as a new-Session default and OpenCode Session model as the authority for subsequent turns. Page selection and `/models` / `/model` call the native Session switch endpoint and ordinary prompts/commands omit model overrides.
+- Evidence: `electron/opencode/client.ts`, `electron/api/routes/opencode.ts`, `src/stores/opencode.ts`, `src/pages/Chat/OpencodeChatPanel.tsx`, focused unit tests, and `tests/e2e/opencode-multichat-runtime.spec.ts`.
+- Future impact: Provider configuration and partner maintenance must remain separate from transient per-Session model selection; future prompt paths must not reintroduce implicit model fallback overrides.
+- Semantic conflicts: none known beyond superseding the previous chat-composer read-only model behavior.
+- Human confirmation required: no; the user explicitly approved parity with OpenCode model switching.