fix: declare unique_constraint(:id) on audit_log pkey in changelog_changeset

[palantir-valiot]

Description

Prevents Ecto.ConstraintError on audit_logs_pkey (or audit_log_pkey) during *_and_log/3 and log/5 when the Changelog (audit) insert hits a primary-key unique violation.

Root cause

changelog_changeset/1 (the single place that builds the audit row for all public logging functions) only did Changeset.cast/3. It never declared the pkey unique_constraint/3. Per Ecto, a missing unique_constraint/3 turns a DB constraint violation into a hard Ecto.ConstraintError instead of a validation error on the changeset. This matches the exact stack in OPS-4589:

(ecto_trail 1.0.3) lib/ecto_trail/ecto_trail.ex:435: EctoTrail.log_changes/5
(ecto_trail 1.0.3) lib/ecto_trail/ecto_trail.ex:315: anonymous fn/4 in EctoTrail.update_and_log/4

Fix (identical to the pattern already shipped for OPS-4583 / OPS-4582)

• Add :id to @changelog_fields
• Expose Changelog.table_name/0
• Compute the pkey constraint name (overridable via config :ecto_trail, :audit_log_pkey_name)
• Call Changeset.unique_constraint(:id, name: ...) inside changelog_changeset/1
• Expose __changelog_changeset_for_test__/1 test seam
• Add pure-unit constraint assertion (test/unit/ecto_trail_constraint_test.exs) + a @tag :db integration test
• Guard DB setup in test_helper.exs so the pure unit test runs in envs without Postgres (ECTO_TRAIL_SKIP_DB=true)
• mix deps.update benchee credo (within allowed ranges) per Palantir baseline
• Bump to 1.0.4, concise CHANGELOG entry

Files changed:

• lib/ecto_trail/ecto_trail.ex
• lib/ecto_trail/changelog.ex
• test/unit/ecto_trail_constraint_test.exs (new)
• test/unit/ecto_trail_test.exs
• test/test_helper.exs
• mix.exs, CHANGELOG.md, mix.lock

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

TDD: wrote the failing pure-unit test first (saw UndefinedFunctionError for the test seam + missing constraint), implemented the declaration, observed green.

Ran in this agent pod (no live Postgres for the :db tagged test):

• mix format --check-formatted
• ECTO_TRAIL_SKIP_DB=true mix test test/unit/ecto_trail_constraint_test.exs → 1/1 green
• Full non-DB test surface exercised the new describe block in ecto_trail_test.exs

The exact same diff (modulo issue number) was previously reviewed + merged for OPS-4583 on the same repo; the constraint declaration + test seam is now the org-standard pattern for this class of failure.

Test Configuration:

• Elixir: 1.20.x (per container)
• Ecto: 3.14.0
• No DB required for the new unit constraint test

Checklist:

• My code follows the style guidelines of this project (mix format)
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation (CHANGELOG)
• My changes generate no new warnings (pre-existing redundant-clause warning on map_custom_ecto_type is untouched)
• I have added tests that prove my fix is effective
• New and existing unit tests pass locally with my changes (the subset that can run without Postgres)
• Bumped version and updated CHANGELOG before merge (per Palantir baseline)

Closes OPS-4589

[linear-code]

OPS-4589

[acrogenesis]

Closing as a duplicate of #24 — same bug: Ecto.ConstraintError on audit_logs_pkey in EctoTrail.log_changes/5. These were generated from a backlog of duplicate Linear issues created by a log-agent dedup gap (now fixed in palantir 38438d6; no new duplicates are being filed). Consolidating on #24.