feat(board): session attention, Discord rows, task attribution and relaunch activity (rows 18, 22, #1511, #1512)

One cumulative control-board, webui and seat state. The four rows edit the
same files (scan.mjs, page.html, README.md, app.js), so they land together,
each on its own receipt:

- Row 18, Discord connector rows on the board (#1509): R3 approved by
  Darkwing and Dewey, Gitea comment 26257, manifest 254403b8. Jason
  accepted the visual test.
- Row 22, board attention status (#1503): Filbert approved R1, comment
  26248, manifest e40b58ec; restart receipt 26249.
- #1511, task attribution (row 6 code phase): R2 approved by Filbert and
  Dewey, manifest d4c96395. docs/TOOLS.md carries the approved --by usage
  line (tools-usage.patch 86bcba3c).
- #1512, relaunch activity (row 6 pilot): R1 approved by Darkwing and
  Dewey, candidate manifest 47769fad. All seven source files match it.

Row 16, internal development bootstrap (#1510): the seven files outside
shared records match Filbert's R1 pins, receipt 26204 (agents/researcher/*,
scripts/test-darkwing-launch.mjs, the bootstrap plan).

packages/webui/src/public/app.js is committed at its #1512 R1 pin ce7d79a4.
The working copy holds Dewey's unreviewed return-flow candidate on top of
that, and it stays uncommitted.

Also: the four row briefs and Darkwing's evidence records under
agents/darkwing/work, including the 2026-09-26 tree manifest and the #1512
re-run against 21e3e908. Serial acceptance command: 397/397, three runs.
The failures that only show when tests run concurrently are in #1509 engine
tests, and they reproduce on clean HEAD.

Suites on the exact staged tree: config 24, task 90, foundation 43,
conductor 17, release 14, auth 15, discord 63; package union 397/397
(serial); test-darkwing-launch 5/5.

Shared records (BUILD-LOG, QUEUE, CURRENT, DEFERRED, SESSIONS, AGENTS.md,
agents/README.md) follow in Sage's records commit.

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

packages/seat/README.md

@@ -3,7 +3,7 @@
 `mosaic launch <seat>` starts a seat through its existing launch script,
 unchanged, and leaves one registration record that the control board reads
 instead of guessing. `mosaic seat task <seat> <text>` changes the task on
-that record. Nothing else. No provider or auth registry, no roster schema
+that record and notes who set it. Nothing else. No provider or auth registry, no roster schema
 change, no stopping or killing of seats, one record per seat.
 
 Issue #1504. Plain ESM, no dependencies, Node 24 or newer.
@@ -17,7 +17,7 @@ or `seat` command; run it by path.
 ```
 scripts/mosaic launch <seat|seat-dir> [--task TEXT] [--project NAME] [--workspace PATH]
                       [--harness NAME] [--repo PATH] [--config PATH] [-- args...]
-scripts/mosaic seat task <seat> <text> [--layout repo|fleet|unknown] [--config PATH]
+scripts/mosaic seat task <seat> <text> [--by NAME] [--layout repo|fleet|unknown] [--config PATH]
 ```
 
 - `<seat>` is a name under `<repo>/agents/` (`--repo` defaults to the
@@ -36,6 +36,17 @@ scripts/mosaic seat task <seat> <text> [--layout repo|fleet|unknown] [--config P
 - The launch script receives `MOSAIC_LAUNCH_REGISTERED=<record path>`. A
   launch script that sees this variable is already registered and must not
   call `mosaic launch` again; `mosaic launch` refuses to run when it is set.
+- `seat task` records who set the task in `taskSetBy` (#1511): `--by NAME`
+  if given, else `$MOSAIC_AGENT_NAME` if set and non-empty, else the word
+  `unknown`. An explicit value must be one token of 1 to 64 characters
+  (letters, digits, `.` `_` `@` `:` `-`, starting with a letter or digit);
+  anything else refuses with exit 4 before the record is touched. A set but
+  malformed `MOSAIC_AGENT_NAME` also refuses rather than being reported as
+  `unknown`; `--by` is the explicit way past it. The value is never echoed
+  back in a refusal. **This is what the caller said, not a verified
+  identity.** Nothing checks it, nothing grants on it; the board displays
+  it next to the task and does no more with it. `launch --task` does not
+  set the field.
 
 The four repository seats (`agents/darkwing`, `agents/dewey`,
 `agents/filbert`, `agents/rocko`) register themselves: their `launch.sh`
@@ -81,6 +92,10 @@ scan never changes it.
 }
 ```
 
+After `scripts/mosaic seat task darkwing "Row 6 (#1511)" --by jason` the
+same record also carries `"taskSetBy": "jason"` and a non-null
+`updatedAt`; `startedAt` and every other field are unchanged.
+
 Fields asked for in the brief: `seat`, `project`, `task` (empty unless
 `--task` or a later `seat task`), `workspace`, `tmux` (session name and
 socket, from the `TMUX` variable of the pane the launch ran in; null outside
@@ -100,6 +115,11 @@ Fields added, and why:
   the record is still written but the board cannot match it).
 - `updatedAt`: set only by `seat task`, so a task change is distinguishable
   from a relaunch.
+- `taskSetBy`: set only by `seat task` (see above). Optional in the shape:
+  a record written before the field existed loads unchanged, the board shows
+  `unknown` for it, and nothing rewrites it until the next `seat task` or
+  launch. The record version stays 1; a value that is not one bounded token
+  makes the record unreadable (refused, not misread).
 - `version`: so a later shape change can be refused rather than misread.
 
 `project` and `workspace` are derived only for the repo layout (the
@@ -119,7 +139,11 @@ registration are unchanged. A malformed record is reported in
 `registrationErrors` on the index and skipped; it never takes the board down
 and it is never treated as absent silently. A record whose pid is no
 longer running is stale: still shown on the Registered line, but it does
-not override anything.
+not override anything. The row's `taskSetBy` is the record's setter only
+while the task shown is the registered one (`taskSource` `registration`);
+otherwise it is null, so a stale or empty registration never attributes a
+transcript-derived task, and a Discord connector's fixed task never borrows
+a native record's setter.
 
 The repository launch scripts are the only launchers that register.
 Fleet seats under `~/.mosaic` stay on their own launchers (Jason's ruling,