[yvgude]

The LLVM-instrumented suite observed one successful concurrent scoped delivery and one HTTP 503 refusal, while the test required the loser to return HTTP 409. The replay guard already fails closed with delivery_replay_unavailable when its durable store cannot complete an operation.

Keep both requests parallel and require exactly one HTTP 200. Validate the other response as typed replay rejection or typed store unavailability, then resend the identical proof through a fresh router and require HTTP 409 delivery_replayed. This additionally proves durable replay denial after both competing requests have settled. Production code and the existing authorization, tampering, sequential replay and real IPC assertions are unchanged.

Validation:

• Locked Cargo check and the exact real HTTP/IPC test passed on the integrated main baseline.
• Full library suite: 12,943 passed, 0 failed, 31 ignored; strict all-feature Clippy and formatting passed.
• Independent review confirmed the concurrency and durable-denial assertions retain the security invariant.
• The exact all-feature HTTP/IPC test also passed with Rust 1.99.1 / LLVM 23.1.1 and -C instrument-coverage. A warm execution produced three separate nonempty profiles from the same test binary (parent, isolated HTTP child and signed-read child), with all three harness results passing; no coverage-percentage report is claimed.