feat(harness): meta-harness and PM launching off T3 (#1523, row 41)

Slice 1 S6. packages/harness runs a role session under the pi or claude
adapter behind a tool gate, and packages/seat holds the session and its
process. The bus host gains a launch socket: `mosaic bus start
<business> --pm <harness>:<model>` runs the PM without a window, the PM
launches role sessions through the broker within the business file's
`launch.max`, and every launch, refusal and end is a launch-log line and
a broker event. `mosaic talk`, `mosaic launches off|on|list` and
`mosaic stop <run>` are new CLI verbs. packages/bus gains the IPC ops
identity, authorize, refuse, endLaunch and credentialStatus, plus
Broker.endLaunch (decision 77); no socket verb, event kind or schema
changed. The session environment is an allowlist, and the runner exits
before claiming if a founder credential reaches it.

Filbert built it (agents/filbert/work/s6). Darkwing reviewed on #1523:
round 1 changes (26991/26995), round 2 changes (27004/27010), round 3
changes (27012/27032), round 4 approve (27033/27034) on manifest
08a78972, 42 paths.

Sage's gate on 64b0f9f1 (12:32Z), sequential and teed: node suites
business 60, bus 74, cli 83, control-board 124, conversation 182,
discord 178, harness 56, ledger 78, mosaic 69, queue 149, runs 41,
seat 27, tasks 51, webui 39, every one 0 failed; test-auth 15,
test-conductor 17, test-config 24, test-discord 66,
test-extension-package 18, test-foundation 44, test-queue 27,
test-release 14, test-task 98 and 26 without Docker, all 0 failed.
64b0f9f1..ee7f909b touches none of the 42 paths. It landed after the
Q14 hold ended at 2026-10-11T17:19:23.857Z. The recorded PM-to-coder
run on a scratch data root is still owed before row 41 moves to done.

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

adapters/pi/adapter.sh

@@ -60,6 +60,19 @@ if [ -n "${MOSAIC_SKILLS:-}" ]; then
     IFS=$OLDIFS
 fi
 
+# Extensions (S6): explicitly provided extension files, loaded with -e
+# after --no-extensions turns discovery off. A missing file refuses here;
+# pi itself also refuses to start on a missing or broken -e (row S0 line 3).
+EXT_FLAGS=""
+if [ -n "${MOSAIC_EXTENSIONS:-}" ]; then
+    OLDIFS=$IFS; IFS=','
+    for e in $MOSAIC_EXTENSIONS; do
+        [ -f "$e" ] || { echo "pi adapter: extension missing: $e" >&2; exit 2; }
+        EXT_FLAGS="$EXT_FLAGS -e $e"
+    done
+    IFS=$OLDIFS
+fi
+
 # Mode (M13): interactive TUI or one-shot print.
 PRINT_MODE="-p"
 REQUEST_ARG=""
@@ -74,13 +87,18 @@ fi
 #                  interactive TUI mode)
 #   --system-prompt  replace the default prompt with the generated one
 #   --no-*         no ambient context/skills/extensions/templates/themes
+#   EXT_FLAGS      the explicitly provided extensions only (-e)
 #   SESSION_FLAGS  ephemeral | persistent | forked (per env)
 #   TOOLS_FLAG     per capabilities
 #   --offline      no startup network operations (update checks/telemetry)
+#   --no-approve   ignore project-local .pi/ files (settings, SYSTEM.md)
+#                  whatever trust is saved for the workspace
 PROMPT_CONTENT="$(cat "$MOSAIC_SYSTEM_PROMPT_FILE")"
 set -- \
     --offline \
+    --no-approve \
     --no-extensions \
+    $EXT_FLAGS \
     $SKILLS_FLAG \
     --no-prompt-templates \
     --no-themes \