Pin the mid-tool-call rule in the control board scanner (#1503)

Acceptance rule (plan page, bf641e22): a seat mid-tool-call is working,
never waiting. The scanner already met it through pi's stopReason values;
deriveState now also checks the content for a toolCall block (working),
after the error stop reasons and before "stop" (waiting). Thinking blocks
do not keep a text turn from being waiting. Three JSONL fixture tests and
three state-table cases pin the rule. Live check on the real board:
orch-01 and rev-code-01 mid-tool-call are working, velma's finished
text-only turn is waiting. Sonnet review: APPROVED.

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

BUILD-LOG.md

@@ -2025,3 +2025,18 @@ under the table is unchanged. Page-only change, one static test
 (control-board 66/66, packages/mosaic 69/69). Sonnet review:
 APPROVED, no findings. Verified in Chrome: "1 of 4", "3 of 4", "4", "13 of 38",
 console clean. Next: Jason keeps using it.
+
+## 2026-09-12 — Control board step 3, mid-tool-call rule (#1503)
+
+Before: the acceptance rule "a seat mid-tool-call is working, never
+waiting" (plan page, commit bf641e22) had no test of its own. The scanner
+met it only through pi's stopReason values.
+
+After: deriveState also checks the message content for a toolCall block
+(working), after the error stop reasons (error) and before "stop"
+(waiting). Thinking blocks do not affect waiting. Three JSONL fixture tests
+and three state-table cases pin it. Suites: control-board 69/69,
+packages/mosaic 69/69. Live check at 14:27Z on the real board: orch-01
+(assistant + toolCall) working, rev-code-01 (tool result last) working,
+velma (text-only, stop) waiting. Sonnet review: APPROVED, no findings.
+No seat changed state because of this change; it closes a gap, not a bug.