Gate D written; brief for piece 4, the WebUI first screen on the Console design (#1506, #1503)

Co-Authored-By: Claude Fable 5.1 <[email protected]>

docs/plans/2026-09-12_control-board-mvp.md

@@ -238,6 +238,63 @@ ledger's output, not from memory.
 - If a number cannot be computed from evidence it prints "unknown", never a
   guess.
 
+## Piece 4: WebUI first screen (Console)
+
+Approved by Jason 2026-09-12 ("speed walk to success") after Gate D. Decision
+MOSAIC-STACK-D-002: Dewey's design 3, Console
+(`agents/dewey/work/wui/mockups/d3-console.html`), is the WebUI starting
+point. The board is its first and only screen. Owner: dewey. Dewey opens the
+issue and updates `CURRENT.md` when picking it up.
+
+### What it is
+
+`packages/webui`: `node packages/webui/src/cli.mjs serve [--port N]
+[--board http://127.0.0.1:7331]`. Loopback only. One page, the Console
+layout from the mockup, populated from the control board's `/api/board`
+JSON: project tree on the left, dense session table (state, task with its
+source tag, active project, workspace, model, registered line, last
+activity), inspector drawer on the row with the last assistant text and the
+reply box. Actions proxy to the board: `POST /api/seen` and `POST /api/reply`
+unchanged in shape. "Simulated" notices from the mockup are gone; every
+control either does the board thing or does not exist yet.
+
+- Data: only what `/api/board` already serves. No new scanner, no new
+  sources, no seat writes. If the mockup shows a field the board does not
+  have, the field is dropped for this piece and a line goes to
+  `docs/plans/DEFERRED.md`.
+- Style: the mockup's CSS and brand assets as they are, palette and
+  appearance switches kept if they are already built, otherwise dropped.
+- Refresh: same as the board page (its scan on load or refresh); no polling
+  loop beyond what the board page already does.
+- No auth, no accounts, no settings page, no second screen, no router.
+
+### Gate E (yes/no)
+
+Jason works Monday 2026-09-14 from the WebUI and does not open the board's
+own page or a terminal to a repo seat to answer "who is waiting on me". Pass
+is his say-so at the end of the day, with any exception written as a line in
+`DEFERRED.md` with the reason.
+
+### Tests
+
+- Page renders the fixture `/api/board` JSON (the board's own test fixture)
+  into the table and tree; counts match the fixture.
+- Seen and reply proxy to the board with the same body; a fake board on
+  localhost captures the requests.
+- Board unreachable: page says so with the URL, no blank screen.
+- Loopback bind only, as the board.
+- Dewey's existing mockup verifier (`work/wui/checks/mockups-verify.mjs`)
+  or its equivalent runs against the served page for contrast and 320px
+  width.
+
+### Boundaries
+
+- `packages/control-board` changes only if the WebUI needs a field the
+  scanner already computes but does not serialize; each such change is one
+  commit with a test, nothing else.
+- No fleet sources, no comms changes, no `packages/seat` changes.
+- Dewey coordinates with Darkwing before touching any board file.
+
 ## How the scanner decides state
 
 The scanner reads the newest pi session log for each agent, plus whether