mcp ask: require the final round's answer; refuse sealed state when the host clock fails (findings 10, 11)

[MattJackson]

Closes MEDIUM findings 10 and 11 in plane-mcp.md.

Finding 10: the state minted for the final ask round, re-sent with no inputResponses, proceeded to the tool because the final redeem ran before the answered check. The answered check now runs first; the refusal spends nothing (spec 379-390).

Finding 11: a failed clock.now was read as 0, so every sealed state (busbar's own and relayed) passed its TTL and fresh states were stamped at the epoch. DoorSeal::now now returns Option and nothing substitutes 0. busbar's own ask refuses with the new ClockUnavailable (ask_clock_unavailable, text names the clock, not the signing key); a relayed ask and a task relay refuse with Unavailable (ask_unavailable) carrying CLOCK_UNAVAILABLE. Relayed-state sealing is one function, seal_relayed, shared by both sites. Fail closed (spec 1576, 3295-3370).

RED plants (fail by assertion on the unfixed tree):

• 6643353: crates/busbar-plane-mcp/src/tests/ask.rs final-round test; tests/door_clock.rs own and relayed state under a failed clock.
• b7fc13f: tests/door_clock.rs relayed ask and task relay refuse as ask_unavailable naming the clock.

Proof (Latchkey): job cli-7fd0ebd0-cd55-4ee6-9342-92c6d4608dbb, RED on b7fc13f exit 1 (the two relay plants fail), GREEN on head adb1d4d exit 0 (fmt, clippy -D warnings, crate tests, root busbar build). Earlier job cli-bc1e7ee9-fe67-456d-b802-926abc4d9a23 proved the 6643353 plants (RED 1, GREEN 0).

Test seam: DoorSeal, Site, decide_ask, seal_relayed are pub and doc(hidden) so an integration test (which may use unsafe host fakes; the lib forbids it) can drive them. No test retired.

[github-actions]

promote into predev: BOARD @adb1d4d5e: 2 failing test row(s), 10 DENY row(s)

Failing tests (2)

crate	test	step	first panic
transport_dropped_in_serves	a_dropped_in_transport_registers_through_the_one_fold_and_serves	test:dropped-in-tcp-transport	crates/busbar/tests/transport_dropped_in_serves.rs:168:13: busbar exited (ExitStatus(unix_wait_status(512))) before serving; log:
-p busbar --test transport_dropped_in_serves	test target failed	test:dropped-in-tcp-transport

DENY rows (10)

gate	row	detail
construction	one-pick-site	3 production call site(s) of 'pick_among(' (ceiling 2): crates/busbar-kernel-egress/src/walk.rs:298; crates/busbar-llm/src/engine/exhaustion/fallback.rs:120; crates/busbar-llm/src/engine/pipeline.rs:8
kind-isolation	kind-isolation:deps	3 finding(s), 93 shipped edge instance(s) over 32 class(es), 93 declaration(s); 57 '[[dep]]' row(s), 0 question(s): unlisted-dep-edge legacy -> plane busbar-llm -> busbar-plane-llm is a shipped edge w
kind-isolation	kind-isolation:test-deps	4 finding(s), 44 test edge instance(s) over 26 class(es), 44 declaration(s); 27 '[[dep]]' row(s), 0 question(s): unlisted-dep-edge cleanliness -> legacy busbar-core-admin -> busbar-a2a is a test edge
kind-isolation-ship	kind-isolation:deps	13 finding(s) over 93 shipped edge(s): ship-edge kernel -> hooks busbar-kernel -> busbar-hook-ranking is 'not-allowed': the architecture grants no kernel -> hooks edge, and the ship criterion is the a
kind-isolation-ship	kind-isolation:test-deps	18 finding(s) over 44 test edge(s): ship-edge cleanliness -> export busbar-core-admin -> busbar-export-prometheus is 'not-allowed': the architecture grants no cleanliness -> export edge, and the ship
kind-isolation-ship	kind-isolation:faces	3 finding(s) over 39 crate(s): foreign-entry crates/busbar busbar is kind 'root' and implements 'Transport' 1 time(s) in shipped source — the entry face of kind 'transport'. A trait implementation is
kind-isolation-ship	kind-isolation:shape	2 deviation(s) over 10 crate(s): entry-count crates/busbar-transport-http busbar-transport-http implements 'Transport' 3 time(s) in shipped source (its 'impl' blocks plus its door tails); every crate
kind-isolation-ship	kind-isolation:legacy-drain	3 finding(s): transitional-live qa/kind-isolation.toml 'busbar-a2a -> busbar-core-admin' (legacy drain: the retiring A2A engine's tests drive the admin surface that drained into the cleanliness tier)
ship-ready	ship-ready:ship-twin	'kind-isolation-ship' is not green: kind-isolation:deps (a dependency the architecture does not grant is still in the graph); kind-isolation:test-deps (a dependency the architecture does not grant is
structure-lint	structure-lint:plane-dup:unledgered	22 finding(s): PLANE-DUPLICATE (module): 'config.rs' — a2a:crates/busbar-a2a/src/a2a/config.rs decisions:crates/busbar-plane-decisions/src/config.rs voice:crates/busbar-voice/src/config.rs (the ledger

Judged against base 2bf9d9b37: 0 new red, 0 worse, 6 standing (excused).

tests passed: 15558, failed: 1. Run: https://github.com/GetBusbar/busbar/actions/runs/37700387361 . Artifact verdict-adb1d4d5e034f301bf654d35dd17882bd61228c9 (failures.json, junit.xml, raw.log; 90 days).