refactor: isolate optional imports and remove dead state

[JNZader]

Search and Intelligence package facades mixed optional-backend probes with public reexports, creating E402 pressure and child-to-facade initialization back-edges. Twelve unused locals also looked like unfinished behavior even though repository output contracts showed they were unsupported state.

This is Slice 2 of the approved three-PR stacked-to-main chain. It restructures optional availability and removes only evidence-backed dead state; mechanical cleanup and Ruff policy remain in Slice 3.

Optional dependency boundaries

• Search now owns backend detection in private _availability.py; core BM25/types/preparation exports remain usable without FAISS.
• Semantic Search exports remain lazy and initialize only when accessed.
• Intelligence now owns parser availability in a private leaf; compressor and extractor registry no longer import the partially initialized package facade.
• Pure/fallback Intelligence surfaces remain available without extras; enhanced registry behavior remains available with extras.
• Clean subprocess tests cover missing, Search-only, Intelligence-only, combined, facade-first, child-first, lazy-load, required-failure, and fault-injection modes.

Evidence-backed F841 dispositions

All twelve approved locals were removed without inventing Built columns, internal-only call filtering, stack-driven setup behavior, AST prompt content, or other latent features. Each row has a named output anchor and a rollback probe that reproduces its original Ruff finding while preserving behavior.

Verification

Measured on refactor/ruff-optional-f841-slice-2 at 509220e:

• Complete suite: 3567 passed, 13 skipped, 88 warnings.
• Slice 2 focused union: 405 passed, 8 skipped.
• Intelligence partition: 405 passed, 5 skipped.
• Broad Search suite: 66 passed, 8 skipped.
• Optional import surfaces: 5 passed.
• F841 output anchors: WU9 150 passed, WU10 91 passed, WU11 69 passed.
• Rollback recurrence: 12/12 rows exactly once.
• Focused E402/F401/F841 Ruff, uv lock --check, and git diff --check: PASS.
• Diff: 16 files, 233 additions, 41 deletions = 274 changed lines.

No build, dependency-version, lockfile, CI, Ruff-policy, suppression, or unsafe-fix change is included. No global Ruff-zero claim is made.

Review trail

• Post-apply Judgment Day: two explicit empty ledgers; APPROVED.
• Formal SDD verification: 4/4 requirement clusters and 14/14 executed behavioral scenarios compliant; zero findings.
• Pre-commit, pre-push, and pre-PR risk sweeps: explicit empty ledgers.
• Open BLOCKER/CRITICAL findings: 0.

Commit structure

Four conventional commits separate optional boundary architecture, display/diagram state, context/setup/graph state, and remaining Intelligence/prompt state. Shared optional-surface tests remain with the structural commit.

Follow-ups noted — not implemented here

Slice 3 will correct the remaining accidental import ordering and mechanical E741/F541 findings, prove the literal pre-policy Ruff-zero gate, then align and pin reproducible local/CI Ruff policy.