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: 1c6b004436
Owner: codex
Status: Ready for Integration

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.

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.

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.

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.

Integration should reconcile the canonical OpenCode Agent readiness and Session model ownership descriptions listed below.

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.

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.