Mirror verified incident receiver v1 contract and conformance fixtures

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The producer connector needs one authoritative receiver contract before automatic delivery can be enabled. This documentation-only change copies the exact JSON contract, prose, 22 frozen receiver fingerprint vectors and SHA-256 manifest from RatelDesk #117, implementing receiver issue #116.

Consumer work: #141 and #152. No connector code, support flags, product version or release behavior changes. Automatic delivery/retry must remain gated until a deployed receiver containing the reviewed merge reports the authenticated capability; current RatelDesk beta.8 is incompatible. The receiver fingerprint is a different projection from the producer Flow fingerprint.

The files match the receiver byte-for-byte. SHA-256: contract 87f534716b4d69619cb9e15f913e896402956e561916f79b1a283dcf635a74b4; fixtures bb6b49ed69ca00bbc6cfe5b226c6ea8858879785eb94945f6a11edf06c947e99; prose f8b67d3b96988cd265d27af7bc4da64fc600589b2cb4ba0a3d4b7a2f8b52b7c5. sha256sum --check docs/contracts/rateldesk-incident-create.v1.SHA256SUMS passes when run from the contract directory. Runtime acceptance is owned by the receiver PR; this mirror does not claim producer integration acceptance.

Final deployment handoff: receiver #117 plus compatibility follow-up #118 are merged at fccae98bd74ac7d7962eb01f4516b44806c758b3. All 17 checks passed on each reviewed PR head and on this final main merge. Main validation and managed PostgreSQL validation are green. Main receiver acceptance: 52 passed, zero failed/skipped (11 SQLite, 11 PostgreSQL, 30 conformance/key); full suite: 1,713 passed, zero failed, six existing skips. Use this final merge SHA for the subsequent compatible build. No release, production deployment, live ticket or tag/latest promotion was produced.

The documentation mirror is merged at 3542928; all 21 current-head and resulting main checks pass. Mirror main validation. Automatic delivery/retry remains capability-gated until an actual compatible receiver build is deployed, its approved source is registered, and its authenticated capability reports rateldesk.incident-create.v1. Existing published beta.8 is incompatible. The next M2M/connector prompts must consume these exact contract/fixture digests; successful authentication alone is insufficient.

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Documentation review of b6a5011 (self-review): fetched the published branch and compared all four contract files against receiver PR #117. Files are byte-identical and every SHA-256 manifest entry verifies. Changes are restricted to docs/contracts; no connector support flag, Flow behavior, release version or workflow changes. Receiver CI has executed 52 acceptance/conformance cases (11 SQLite, 11 PostgreSQL and 30 golden/key cases), zero failures/skips. Producer delivery remains capability-gated until the reviewed receiver is actually deployed. No substantive finding in this documentation diff.