fix: handle audit_logs_pkey unique constraint in log_changes (OPS-4574)

[palantir-valiot]

Summary

Root cause: update_and_log / insert_and_log (and friends) run inside an explicit repo.transaction, then call log_changes which does a raw repo.insert(changelog_changeset(...)). The Changelog schema had no unique_constraint declared on its pkey, so a DB unique violation on audit_log_pkey (e.g. sequence rewind in prod) produced an unhandled Ecto.ConstraintError instead of {:error, changeset}. The surrounding code already treats {:error, reason} as a soft failure (it logs and returns {:ok, reason}), allowing the caller's write to succeed. The error surfaced in valiot_app during a GraphQL updateDevice mutation.

Fix: pipe the cast through Changeset.unique_constraint(:id, name: pkey_constraint_name()) inside changelog_changeset/1. The pkey name is computed dynamically from the (configurable) Changelog table source so it works for custom table_name configs. Added a TDD test that seeds a Changelog row, rewinds the sequence, then calls update_and_log and asserts the outer operation still succeeds.

Changed files:

• lib/ecto_trail/ecto_trail.ex:574 (the constraint declaration + helper)
• test/unit/ecto_trail_test.exs (new collision test in the update_and_log describe)
• mix.exs, CHANGELOG.md (version + release note)
• mix.lock (freshened dev/test deps per baseline rules)

Why

This is the exact failure described in OPS-4574 (Ecto.ConstraintError on audit_logs_pkey during ecto_trail.log_changes called from update_and_log inside a transaction). See stack trace in the issue for lib/ecto_trail/ecto_trail.ex:435.

Closes OPS-4574

Test plan

• mix format (clean)
• mix compile (clean; only pre-existing redundant-clause warning in map_custom_ecto_type)
• mix hex.outdated + upgraded benchee 1.5.0→1.5.1 and credo 1.7.18→1.7.19 (and transitive) within allowed ranges in the same commit
• Added/edited a regression test that forces a pkey collision on the audit log table (via setval on the sequence) during update_and_log and asserts success instead of ConstraintError
• mix test — could not execute in the agent pod (Postgres is not available on localhost:5432; test/test_helper.exs requires a real DB and runs migrations). The new test follows the exact style and helpers of the surrounding tests and will be exercised by CI.
• Read git diff; no debug prints, no unrelated changes, no empty diff
• Version bump 1.0.3 → 1.0.4 and concise CHANGELOG entry (one line describing the visible behavior shift)
• Branch name follows the non-negotiable convention: palantir/OPS-4574-handle-audit-log-pkey-constraint
• PR body written from scratch (not the raw template)

Screenshots

N/A — no UI change.

[linear-code]

OPS-4574

[acrogenesis]

Closing as a duplicate of #24 — all of these PRs fix the same bug: Ecto.ConstraintError on audit_logs_pkey in EctoTrail.log_changes/5. They were filed by a log-agent dedup gap (the same exception, wrapped in a structured-log JSON envelope with varying doc/request_id/params, hashed differently each time). That gap is now fixed in palantir (commit 38438d6) so this won't recur. Consolidating on #24.