SEP-2011: Teach the duplicate-check precheck to read unique constraints

[Copilot]

BaseSQLModelManager.save's duplicate precheck introspected local_table.indexes only, so the four tables that declare uniqueness as a UniqueConstraint in __table_args__ (syncentityabsence, taskhistory_log, taskhistory_log_state, atw_incident_execution) fell through to commit and answered HTTPBadRequestException (400) where every index-declared table answers HTTPConflictException (409).

app/core/db/crud.py

• The precheck now runs one loop over the union of unique column-sets from both sources — each unique Index.columns and each UniqueConstraint.columns — so the body that builds equal_filters, queries, and raises stays written once and the message format ("<Model> with the same <columns> already exists") is identical either way. PrimaryKeyConstraint is excluded by the isinstance filter.
• The completeness test moved from truthiness to presence:

if all(value is not None for value in equal_filters.values()):

A naive port would have kept all(equal_filters.values()), which silently skips any key whose column holds 0 — i.e. taskhistory_log's most common row, the first chunk of a stream at start_offset=0. This narrows the skip condition on the pre-existing index path too, so it can only start catching collisions that were previously missed.

tests/app/core/db/test_crud.py

• New ConstraintUniqueModel / ConstraintUniqueManager mirroring the CompositeUniqueModel pattern but declaring a single-column and a composite unique key via UniqueConstraint, with one column that legitimately holds 0.
• Cases in TestSaveDuplicatePrecheck for a single-column collision, a composite collision (a leading-column-only match still saves), a collision whose key member is 0, no write emitted before the conflict, and an update to a free value. All four failing cases reproduce the 400 with the crud.py change reverted.

changelog.d/SEP-2011.fixed.md

• User-facing status-code change, added via make changelog-add.

No schema change: migrating the four declarations to unique Index objects was the alternative, but it needs Alembic migrations across two tracks and does nothing for the next UniqueConstraint-only table added.

[Copilot]

🟡 Changes recommended

The shared behavior change leaves stale truthiness contracts and needs a complete caller audit.

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Pull request overview

Expands duplicate prechecks to cover SQLAlchemy unique constraints and valid falsy key values.

Changes:

• Combines unique indexes and constraints in duplicate detection.
• Adds regression coverage for constraint collisions.
• Documents the resulting 409 response behavior.

File summaries

File	Description
app/core/db/crud.py	Expands duplicate-key discovery.
tests/app/core/db/test_crud.py	Adds constraint-path tests.
changelog.d/SEP-2011.fixed.md	Records the user-facing fix.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Balanced

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