chore: add planning notes for brand kit and agent starter work

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

task_plan.md

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+# Task Plan: Server-Backed Brand Kit Canvas Context
+
+## Goal
+Persist Brand Kits by authenticated user, bind one optional Brand Kit to each project/canvas, expose a canvas-header selector, and make every Agent Chat turn and newly created thread use the selected kit as authoritative creative context.
+
+## Current Phase
+Phase 5
+
+## Phases
+
+### Phase 1: Architecture Discovery
+- [x] Map Brand Kit frontend state, project persistence, chat/thread creation, and generation context flow
+- [x] Confirm API generation, storage-driver, schema, and test patterns
+- **Status:** complete
+
+### Phase 2: API and Domain Design
+- [x] Update the `.api` contract before generated code
+- [x] Define user-owned Brand Kit storage and project binding invariants
+- [x] Define server-side prompt injection behavior for all project chat sessions
+- **Status:** complete
+
+### Phase 3: Backend Implementation
+- [x] Generate handlers/types from the validated API specification
+- [x] Implement memory and PostgreSQL Brand Kit persistence keyed by user ID
+- [x] Persist and expose project `brandKitId`
+- [x] Inject selected Brand Kit into Agent Chat and new-thread context
+- [x] Add backend tests and API documentation
+- **Status:** complete
+
+### Phase 4: Frontend Integration
+- [x] Replace local-only Brand Kit persistence with authenticated API persistence
+- [x] Add canvas-title Brand Kit selector with None and user-owned kits
+- [x] Add a Brand Kit selector to the Home prompt composer, including an empty create action
+- [x] Keep Brand Kit editor, defaults, and project binding synchronized
+- **Status:** complete
+
+### Phase 5: Verification
+- [x] Run API validation, generation checks, Go tests/build, frontend typecheck/build
+- [ ] Verify CRUD, user isolation, project binding, chat context, and selector behavior
+- [ ] Inspect desktop and mobile browser layouts
+- **Status:** in_progress
+
+### Phase 6: Delivery
+- [ ] Review scope, generated files, and prohibited product references
+- [ ] Provide preview URL and concise implementation notes
+- **Status:** pending
+
+## Invariants
+- Brand Kits are owned and queried only through the authenticated user ID from request context.
+- A project may reference zero or one Brand Kit owned by the same user.
+- Selecting None clears the binding without deleting the Brand Kit.
+- Server-side Agent Chat context is derived from the persisted project binding, never trusted from a client-supplied prompt.
+- Home may request a Brand Kit ID only from the authenticated user's list; the server revalidates ownership before binding it.
+- Deleting a Brand Kit clears project bindings to it.
+
+## Errors Encountered
+| Error | Attempt | Resolution |
+|-------|---------|------------|
+| zsh rejected an unmatched `HomePage/*.css` glob | 1 | Replaced the glob with explicit files discovered via `rg --files`. |
+| Assumed `CanvasWorkspace/index.css`, which does not exist | 1 | Locate the workspace stylesheet from its imports before reading it. |
+| `rg` treated a pattern beginning with `-- name:` as a flag | 1 | Use `rg -- <pattern>` when searching SQLC query annotations. |
+| Assumed `AuthProvider.tsx` instead of the component directory entry | 1 | Locate the file with `rg --files` before any further auth-provider reads. |
+| PostgreSQL package test failed after adding project mapping because text conversion helpers were not yet defined | 1 | Add nullable `pgtype.Text` conversion helpers and rerun the package tests. |
+| One patch to remove a temporary `err = nil` line used the wrong surrounding field name | 1 | Reapplied the patch against the exact current lines; no code change was lost. |
+| Workspace import patch assumed a nonexistent `BrandMark` import | 1 | Located the actual import block and applied the selector change against current source. |
+| First i18n patch used an inexact Chinese source string | 1 | Re-read the locale file and patched the exact key/value context. |