flake: malformed-B cleanup witness races the child's feedback prompt count #1042

During #1005 development, the new malformed-response-result cleanup witness passed and then failed without a source change between those runs.

Local command, run twice:

timeout 90 deno test --allow-all --frozen packages/cli/tests/repl-headless-clients.test.ts

Runtime: Deno 2.9.7 / V8 15.0.245.2-rusty / TypeScript 6.0.3, macOS aarch64; Node v26.5.1 for ACP subprocesses. These were local runs, so there is no Actions run URL.

• 2026-10-31 23:45:51–23:46:36 UTC: actual test exit 0; 1 test, 14 steps passed.
• 23:46:40–23:47:25 UTC: actual test exit 1; malformed-B-result step failed at expect(held.host.fake.prompts).toHaveLength(1), receiving two prompts. The other 13 steps passed.
• The first prompt is the original request. The additional observed prompt contains the accepted answer, consistent with the child's ordinary feedback continuation. This observation alone does not establish a resend or a production defect.

Candidate provenance: clean base fa3b389d7a05bb4aab1f860127a200c4d61ac29b plus uncommitted test changes; these runs are not claimed against the clean base. The identical client-test file has SHA-256 01feab902d7b17fd1a1d21998d4fe290839923cbaf207dea8bb84e3a2295ce80. Successful native edit replay reconstructed that candidate and matched the subsequent working file after its recorded edits; there was no intervening source edit between pass and failure.

The first complete test outputs and native command/edit chronology are retained in the integration evidence. A later candidate permits one or two prompts, but that change still needs review: distinguish the legitimate feedback prompt from resubmission, preserve the original malformed-result cause and prove joined cleanup and child continuity. A green rerun alone does not close this issue. Close only after the cause and regression evidence are recorded in the delivered correction.