test(preflight): #357 backfill — de-mock test_preflight_dedup_v2.py + decrement trap cap 8→5

[silongtan]

Summary

First trap-row backfill PR driven by the #359 sub-task 1 audit. Converts the two integration tests in `tests/test_preflight_dedup_v2.py` from `MagicMock`-based ctx to a real `memory://` SurrealDB adapter. Drops trap count from 8 to 5 in one go — all three preflight-cluster traps (`get_decisions_for_files`, `get_collision_pending_decisions`, `get_context_for_ready_decisions`) flip from solitary to direct-sociable.

What changed

`tests/test_preflight_dedup_v2.py`:

• New `_fresh_real_ctx` helper: builds a per-test `memory://` SurrealDB with schema migrated, returns the ctx + client
• The 9 pure-function tests stay solitary (testing pure functions — correct posture)
• The 2 integration tests are now `async def` and use the real adapter
• Retained narrow-seam mocks (per CLAUDE.md):
  • `ledger.queries.get_ledger_revision` — the SPECIFIC failure/success behavior under test
  • `handlers.sync_middleware.ensure_ledger_synced` — keeps the auto-sync from touching the working tree

`tests/test_ledger_mock_regression.py`:

• `EXPECTED_TRAP_CAP`: 8 → 5 (locks in the one-way-ratchet improvement)

Audit impact

Category	Before	After	Δ
Direct sociable	24	27	+3
Solitary trap	8	5	-3
Indirect sociable	25	25	0
Uncovered	0	0	0

The three preflight-cluster trap rows are gone. Remaining traps are in two clusters:

• remove_source (4 fns): `decision_exists`, `get_decisions_for_span`, `input_span_exists`, `get_input_span_row`
• link_commit (1 fn): `get_region_metadata`

Out of scope

• `tests/test_preflight_dedup_telemetry.py` and `tests/test_v055_region_anchored_preflight.py` still mock the preflight-cluster functions, but they no longer contribute to trap status (every preflight function is now sociable-covered via this PR's de-mocked tests). They get optional follow-up PRs.
• The remove_source and link_commit cluster traps are separate follow-up PRs.

Verification

```
$ pytest tests/test_preflight_dedup_v2.py
18 passed in 0.77s

$ pytest tests/test_ledger_mock_regression.py
3 passed
```

Ruff check + format clean.

Test plan

• CI green
• Adjacent: `tests/test_preflight_dedup_telemetry.py` and `tests/test_v055_region_anchored_preflight.py` unchanged → no regression

🤖 Generated with Claude Code

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