feat(conversation): CHAT-03 I1, mediated control of a sealed headless Pi (#1507)

Controller, claim store, live-session guard, engine link and seal,
turn tracker, cohort force stop and recovery, client library,
transcript and mediated terminal, with the fake engine and tests.
Fixtures only; no live cutover.

Dewey built it. Darkwing (comment 26690) and Filbert (comment 26694)
approved round 2. Manifest I1-r2-manifest.sha256 (2b48e333, 27 files).
Suites on an export: conversation 152/152, control-board 124, webui 14,
seat 19, chat-00/01/01c checks, and all nine scripts/test-*.sh green.
Follow-ups for I3 are in DEFERRED. Gate E stays with Jason.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

BUILD-LOG.md

@@ -3546,3 +3546,20 @@ Manifest `agents/dewey/work/chat-03/I1-r2-manifest.sha256` (2b48e333, 27
 files), packet `agents/dewey/work/chat-03/BUILD-I1-r2.md`. Row 5 back to
 in-progress (rev 56), then in-review round 2 (rev 57); request posted as
 comment 26689 on #1507 (rev 58). Nothing committed or pushed.
+
+## 2026-10-04: CHAT-03 I1 committed (#1507, row 5, Sage)
+
+Darkwing (comment 26690) and Filbert (comment 26694) approved round 2,
+with nothing to fix before the commit. Sage checked the 27 files against
+manifest `I1-r2-manifest.sha256` (2b48e333, 27 OK) and ran every suite on
+an index export with the candidate laid over HEAD, one run each, output
+kept in `~/sage-scratch/r5-out/`:
+- conversation 152/152, control-board 124/124, webui 14/14, seat 19/19;
+- the chat-00 (48), chat-01 (R3) and chat-01c checks pass;
+- auth 15, conductor 17, config 24, discord 64, extension-package 18,
+  foundation 44, release 14 and task 90 pass;
+- queue 27 passes with node 148/148. Its two live checks skip outside the
+  canonical root.
+
+The reviewers' follow-ups are in DEFERRED for the I3 brief. Row 5 goes to
+waiting-on-jason for Gate E.