test(OMN-13593): pin delegation_events.context_pack_hash migration vendoring guard

[jonahgabriel]

OMN-13593 — delegation_events projection 503: pin context_pack_hash migration vendoring guard

Closes the schema-drift class that DLQ'd 4 delegation projection topics on the stability lane with column "context_pack_hash" of relation "delegation_events" does not exist and returned HTTP 503 degraded.

Root cause: stability-lane-lag, NOT missing-migration-on-dev-HEAD

The node-owned migration 0020_delegation_context_pack_hash.sql (OMN-13407, vendored under #2065) is present on dev-HEAD and verified applied on the dev lane (read-only psql probe of omnibase-infra-postgres):

• omnidash_analytics.delegation_events HAS the context_pack_hash column (text)
• node:node_projection_delegation:0020_delegation_context_pack_hash.sql is tracked in public.schema_migrations

So the migration applies correctly via the forward-migration runner; the stability-lane 503 is an image/warm-volume lag the redeploy workstream clears — not a source defect.

What this PR changes (source)

Unlike every prior delegation migration (0017/0018/0019), 0020 had no vendoring regression guard. A future sync-node-migrations.sh re-vendor or renumber could silently drop it from the deployed forward tree and re-introduce this exact drift on the next fresh deploy. This PR adds test_context_pack_hash_migration_vendored to TestVendoredViewMigrations, pinning the migration permanently so a fresh deploy always materializes the column.

• Proven by TDD: FAILS with 0020_delegation_context_pack_hash.sql must be vendored when the migration is moved aside (the exact fresh-deploy failure mode), PASSES when vendored.
• Asserts the file exists, the column add is idempotent (ADD COLUMN IF NOT EXISTS context_pack_hash TEXT NOT NULL DEFAULT '' — warm volumes reconcile), and the supporting index is present.
• Full tests/unit/migrations/ green (41 passed, 1 skipped) in CI-equivalent env; mypy clean on the changed test file. Test-only diff.

DoD note

DoD item 3 (4 topics return HTTP 200 on fresh redeploy) is a runtime redeploy owned by the redeploy workstream on a lane running the full projection API stack (stability/prod). This PR lands the source-side permanent guard + the dev-lane root-cause proof; no prod/stability/judge runtime mutation here.

Evidence-Source: OCC#3144
Evidence-Ticket: OMN-13593

Paired OCC receipt PR: OmniNode-ai/onex_change_control#3144 (contracts/OMN-13593.yaml + PASS dod_receipts).

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

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Run ID: d90a8d6f-d643-4887-aba4-e92d80b4e9ea

📥 Commits

Reviewing files that changed from the base of the PR and between 6d99d5b and de96585.

📒 Files selected for processing (2)

• docker/migrations/forward/nodes/node_projection_instruction_eval/0001_create_instruction_eval_aggregate_snapshots.sql
• tests/unit/migrations/test_node_migration_discovery.py

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch jonah/omn-13593-delegation-context-pack-hash-migration-guard

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