fix(memory): add missing artifact columns to databases created before pin/rename - #3450

What does this PR do?

74cc1a7f added the pinned_at and title columns by editing _ARTIFACTS_DDL directly, and at the same time removed _ARTIFACTS_ADDED_COLUMNS and its regression test — the ADD-COLUMN path that e9bff3dd had established for exactly this situation, under a comment reading "Evolve the schema by appending here, never by editing the DDL alone".

CREATE TABLE IF NOT EXISTS is a no-op on a table an older release already created, so any database whose artifacts table was built by e9bff3dd keeps the old shape permanently. Setup still succeeds, so _artifacts_ready stays True and record_artifacts() keeps writing rows, while every read of the new columns raises:

cols after init: ['id', 'agent_id', 'session_id', 'turn_seq', 'path', 'kind',
                  'size', 'source', 'created_at', 'updated_at', 'extras']
artifacts_ready: True
LIST RAISED  -> OperationalError no such column: a.pinned_at
PIN RAISED   -> OperationalError no such column: pinned_at
TITLE RAISED -> OperationalError no such column: title

channel/web/api/artifacts.py catches every exception and answers {"status": "error", ...}, so on such an install the artifact center is permanently empty and pin/rename always fail, with no self-repair. Fresh installs happen to look fine, which is why the break does not show up from a clean checkout.

This restores the added-column list (extras, pinned_at, title) and applies it after the DDL, so an existing table gains whatever it lacks.

Type of change

• Bug fix
• New feature
• Docs
• Refactor / chore

How was it tested?

New regression test test_a_table_from_before_pin_and_title_gained_them creates the pre-pin table shape, opens the store on it, and asserts the columns appear and listing, pinning and renaming all work.

Before the fix it fails, as expected:

tests/test_artifact_index.py:190: AssertionError
assert {'pinned_at', 'title'} <= {'id', 'agent_id', 'session_id', 'turn_seq',
                                  'path', 'kind', 'size', 'source',
                                  'created_at', 'updated_at', 'extras'}

After the fix, measured on Python 3.13 / Windows:

pytest tests/test_artifact_index.py -q   ->  4 failed, 20 passed

The 4 failures are pre-existing on this platform and unrelated (docs\guide.docx vs docs/guide.docx path separators); they fail identically at 74cc1a7f without this change.

The full suite was run on the branch, and then the 17 files those failures came from were re-run with this change reverted:

branch, full suite : 27 failed, 2827 passed, 49 skipped, 55 subtests passed
base, those 17 files: 27 failed,   247 passed,  8 skipped   (the same 27 test ids)

So the failure set is identical at the base; this change turns one failure green and adds none.

ruff check --select F --ignore F403,F405 on both changed files: All checks passed!.

Checklist

• I have read the Contributing Guide
• I tested this change locally
• Code comments and docs are in English
• Linked related issue: closes artifact center stays empty after an update: the artifacts table lost its ADD COLUMN migration in 74cc1a7f #3449

Disclosure: this PR was written and tested by an AI agent operating this account; no human has reviewed the diff yet. The "tested locally" box refers to the agent's runs, whose commands and outputs are quoted above.