Extract EditorState from AppLayout (step 3a)

.claude/sessions/2026-04-06.md

@@ -166,3 +166,110 @@ Full plan at `.claude/plans/architecture-refactor.md`. Key points:
   - Existing `ConversationHistory.spec.ts` tests become the spec for `Conversation`
   - Rewrite tests to follow convention, then migrate implementation
   - `AgentRun` receives `Conversation`; `AnthropicAgent` creates both
+
+
+---
+
+## Session continuation 3 (same day, later still)
+
+This continuation picks up from compact. The previous session had just planned step 1a as the next move. We worked through steps 1a → 3a over several PRs, with one architecture plan revision along the way.
+
+---
+
+### 1. Step 1a — `Conversation` / `ConversationStore` split (PR #183)
+
+Already completed before context compacted, but recorded here for continuity. Split `packages/claude-sdk/src/private/ConversationHistory.ts` into:
+- `Conversation.ts` — pure data: stores `HistoryItem[]`, merge logic, compaction, no file I/O
+- `ConversationStore.ts` — I/O wrapper: reads/writes `history.jsonl`, holds a `Conversation` instance
+
+`AgentRun` receives a `Conversation`; `AnthropicAgent` creates both `ConversationStore` and extracts the inner `Conversation` to pass down. Tests migrated to `Conversation.spec.ts` following the one-expect-per-it convention.
+
+---
+
+### 2. Five banana pillars restoration (PR #185)
+
+Philosophy document `.claude/five-banana-pillars.md` was lost at some point after commit `b67b1f6`. Content recovered from git history and restored. No code changes.
+
+---
+
+### 3. Step 1b — Replay conversation history into TUI on startup (PR #186)
+
+New file: `apps/claude-sdk-cli/src/replayHistory.ts` — `replayHistory(messages, emit)` converts `BetaMessageParam[]` into the `StreamEvent` shapes that `AppLayout` already handles, replaying them into the conversation view so prior turns are visible when the CLI starts.
+
+`runAgent.ts` calls `replayHistory` after constructing the agent and before entering the input loop. The history is read via `agent.getHistory()`.
+
+Effect: starting the CLI mid-conversation now shows the previous exchange in the TUI rather than a blank screen.
+
+---
+
+### 4. Step 2 — `RequestBuilder` extraction from `AgentRun` (PR #187)
+
+New file: `packages/claude-sdk/src/private/RequestBuilder.ts` — pure function `buildRequest(conversation, options)` that assembles the Anthropic API request body from current history and run options. No I/O, no side effects.
+
+`AgentRun` now delegates request construction to `RequestBuilder`. The split makes request logic independently testable and separates "what to send" from "how to run the loop".
+
+---
+
+### 5. Architecture plan revision — MVVM without data bindings (PR #188)
+
+The original plan used a component-based approach. After reading the code more carefully, this was revised to a cleaner MVVM model with three explicit layers:
+
+- **State** — pure data and transitions (`EditorState`, `ConversationState`, etc.). No rendering, no I/O.
+- **Renderer** — pure functions `(state, cols) → string[]`. Know column width but not row position. Testable with plain string assertions.
+- **ScreenCoordinator** — owns the physical screen. Handles events (keypress, stream data, resize). After each event: updates relevant state, calls all renderers, allocates rows, assembles and writes output. Single trigger for re-renders.
+
+Key properties this design gives us:
+- Reflow lands cleanly: state untouched on resize, renderers re-called with new `cols`, coordinator re-allocates rows
+- State machines testable without any ANSI knowledge
+- Renderers testable with plain string assertions
+- Cross-component layout constraints (tool widget expands → conversation shrinks) live in coordinator — one place
+- Pull-based and explicit: no data bindings, no reactive subscriptions
+
+The distinction between Renderer and Coordinator: Renderer knows *what* is on screen (content, colours, wrapping) and takes `cols`. Coordinator knows *where* it goes (row position, cursor placement) and takes both `cols` and `rows`.
+
+Plan file updated at `.claude/plans/architecture-refactor.md`.
+
+---
+
+### 6. Step 3a — `EditorState` extracted from `AppLayout` (PR #189, pending merge)
+
+New file: `apps/claude-sdk-cli/src/EditorState.ts`
+
+```typescript
+export class EditorState {
+  #lines: string[] = [''];
+  #cursorLine = 0;
+  #cursorCol = 0;
+
+  public get lines(): string[]   // live internal array — intentionally mutable until 3b
+  public get cursorLine(): number
+  public set cursorLine(n: number)
+  public get cursorCol(): number
+  public set cursorCol(n: number)
+  public get text(): string      // lines.join('\n')
+  public reset(): void           // lines=[''], cursor at 0,0
+}
+```
+
+`AppLayout` changes:
+- `#editorLines`, `#cursorLine`, `#cursorCol` fields removed
+- `#editorState = new EditorState()` added
+- Two reset sites (`completeTurn`, `waitForInput`) replaced with `this.#editorState.reset()`
+- All field accesses updated to go through `#editorState`
+
+Key handling and rendering still live in `AppLayout` — behaviour is identical. The `lines` getter intentionally returns the live internal array because `AppLayout` still mutates it via index assignment and `splice`. This is documented as temporary until step 3b.
+
+BananaBot approved. PR #189 open, auto-merge set to squash.
+
+---
+
+### State at compact
+
+- Branch: `feature/editor-state`, one commit ahead of main (`c020b84`)
+- PR #189 open, approved, awaiting merge
+- **Next: step 3b** — move key handling into `EditorState.handleKey(key: KeyAction)`
+  - `handleKey` returns `boolean` (true = handled, false = AppLayout handles it)
+  - `#wordStartLeft` / `#wordEndRight` helpers move into `EditorState`
+  - `ctrl+enter` stays in `AppLayout` (involves attachments and `editorResolve`, not pure state)
+  - AppLayout key dispatch becomes: delegate to `handleKey`, schedule render, then handle `ctrl+enter` separately
+  - Tests: pure state machine → valuable unit tests for backspace, enter, ctrl+left, ctrl+backspace, delete, up/down clamping