[fm] Introduce SitrepGuardedInsert.#10564
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Add the `SitrepGuardedInsert` Diesel combinator and the
`SitrepGuardedResource` trait: a generic primitive for FM rendezvous to
insert a resource row idempotently and guarded against stale-sitrep
execution.
The combinator wraps a caller-supplied resource INSERT in a single CTE
statement that:
- aborts (StaleSitrep) unless the executor's expected generation still
equals the latest sitrep's generation column;
- short-circuits (AlreadyExists) if a creation marker already exists for
the resource id;
- on a successful insert, atomically writes a creation marker, gated by
`WHERE EXISTS (SELECT 1 FROM new_resource)` so a marker is never
fabricated for a pre-existing row.
All spliced SQL identifiers come from the trait's `&'static str` consts, so
the query is injection-safe. The result is surfaced as a
`SitrepGuardedInsertOutcome` of Created / AlreadyExists / StaleSitrep.
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This was referenced Jun 8, 2026
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Remember to hold off on merging until the gate re-opens, but otherwise LGTM
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Add the
SitrepGuardedInsertDiesel combinator and theSitrepGuardedResourcetrait: a generic primitive for FM rendezvous to insert a resource row idempotently and guarded against stale-sitrep execution.The combinator wraps a caller-supplied resource INSERT in a single CTE statement that:
WHERE EXISTS (SELECT 1 FROM new_resource)so a marker is never fabricated for a pre-existing row.Context: #10248. This PR was previously #10532 but I made a mess of it. This is used in #10533 and #10535 which are split out in hopes of making the review somewhat less miserable.