docs(agents): web todo display Agent Note — side-effect channel + two surfaces

2026-07-23 13:54:33 +08:00
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+# Agent Note: Web todo display — snapshot side-effect channel + two render surfaces
+
+Status: implemented
+
+English | [中文](2026-07-23-web-todo-display.zh.md)
+
+## Problem
+
+`todo_write` appends `todo/write` whole-list snapshots to the session log; the TUI renders a persistent plan panel and the ACP bridge maps the event to native `plan` updates. The web client dropped the event entirely: the host mux stream already forwards every session event, but `todo/write` is not a surface type (it never folds into `ConversationSnapshot.nodes`), and no side-effect branch accumulated it — the browser had no consumption point and no display surface.
+
+## Decision
+
+Consume `todo/write` as a Session side effect, not a surface node, and render it on two surfaces matching the split the TUI and ACP already draw.
+
+### Side-effect channel, converging with window replay
+
+`applyEventSideEffects` gains a `todo/write` case (whole list, last write wins) and `rebuildDerivedFromWindow` resets it, so the live path and every window rebuild (paging, reconnect stitch, resync) converge on the same latest snapshot — the same shape partial/openCalls already use. `ConversationSnapshot.todos` is the read surface. This follows the event's own contract ("log-only UI state; never derived history"): surfacing each write as a conversation node would render superseded lists as if they were still standing.
+
+### TodoPanel: the durable list as a persistent strip
+
+The skeleton pins the panel between the view area and the composer (the composer-card axis), hidden while empty, collapsible with the in-progress item as the collapsed one-line hint; ✓/●/○ glyphs mirror the TUI plan panel. It reads `snapshot.todos` via the framework `useSession` hook — no store, no service, no ctx. It lives inside `ConversationRoot` rather than the details column or its own slot: the details slot is single-occupant and selection-driven (a different lifetime than an always-on strip), and the slot table reserves no plan seat. The component is props-complete and framework-free, so a later relocation to a dedicated slot touches nothing inside it.
+
+### TodoRow: the per-call row through the toolview registry
+
+The dedicated `todo_write` chat row registers through the named `ctx.toolviews` registry from `apply` (the cross-domain assembly point, the same posture as the bash samples but a product registration). The summary derives from call args (`N/M done · active item`); unparseable args fall back to the generic row summary; clicking opens the details column with the raw args. No `ToolEventView` is added for todo — presentation is client-owned, and the durable list renders from the session event, not the tool card.
+
+## Alternatives considered
+
+- **Fold todo writes into `nodes` as surface entries** — replayed windows would render every superseded list; the event is deliberately not a surface type.
+- **Details column or a dedicated slot for the panel** — the details slot is single-occupant and selection-driven; a new slot key needs a slot-table seat that design has not assigned. The panel is framework-free, so the relocation stays cheap if one lands.
+- **Host-computed view (a todo `ToolEventView`)** — presentation belongs to the client; the wire already carries the whole snapshot in the event payload.
+
+## Consequences
+
+Replay correctness is owned by one code path: any future change to window rebuild keeps todos consistent for free, and the fixture (fx-alpha turn 63) plus `scripts/verify-todo-display.mjs` pin the full chain (panel visibility, row summary, details linkage, collapse, dark theme) in a real chromium. `todos` is a required `ConversationSnapshot` field, so scripted fakes in specs must carry it. The ACP bridge's todo → `plan` mapping and the TUI panel are untouched; the web surfaces render the same event with no new wire vocabulary.