fix(daemon): cap Librarian input + auto-repair broken wikilinks

[nickroci]

Summary

Two independent daemon fixes, one per commit.

1. Librarian re-scanned the WHOLE session (wasteful + crashed it)

The Librarian fed every turn of a session to the model each pass, pushing prompts to 259K chars (median 71K). That drove cost (~$100/2 days) and OOM-killed the spawned SDK subprocess (8× Fatal error in message reader: exit code -N). Re-scanning the whole session is pointless — learned material is already persisted in the library.

• New named, tunable module constant ROLLING_BUFFER_BUDGET_TOKENS = 30_000 (ROLLING_BUFFER_MAX_CHARS = 120k chars at 4 chars/token) in librarian_prompt.py.
• cap_buffer_to_recent() keeps the most-recent turns within budget, drops the oldest, always retains ≥ the single newest turn, and logs the dropped count.
• buffer_to_prompt_text() applies the cap so the formatted block — and thus prompt_chars — is bounded; the returned flat list is the same capped window so downstream consumers agree with what the model saw.

2. Broken wikilinks were DETECTED but never REPAIRED

check_invariants only WARNED. A hallucinated phantom index.md row (projects/some-fake-project/...) re-tripped the warning on every run (47×). The pre-write guard in llm._make_path_guard only inspects prospective Write/Edit content, so a phantom link already on disk that the Scholar doesn't rewrite this pass is never touched.

• New scholar_prompt.repair_broken_wikilinks(): deterministic, idempotent post-write pass (sibling to reconcile_readmes) that removes phantom index.md catalog rows, resolves broken body links to a unique existing entry by leaf-name match (alias preserved), or neutralises unresolvable links to plain text without destroying surrounding prose.
• Wired into scholar.review via _repair_wikilinks_safe, running BEFORE the invariants check so the safety net confirms broken-wikilink violations drop to zero.
• Verified against a read-only copy of the live store: the real some-fake-project phantom was the ONLY broken-wikilink violation; repair removed exactly that row (1→0), preserved all 196 other rows, and a second pass is a no-op. The live daemon will self-heal it on its next run (no hand-editing of the live store).

Test plan

• uv run --frozen ruff check . && uv run --frozen ruff format --check . — clean
• uv run --frozen pyright — 0 errors (strict on source; pre-existing __main__ warning unrelated)
• uv run --frozen pytest — 538 passed, 90.11% coverage (≥90 gate)
• duplicate-code gate — no findings (10.00/10)
• New tests: 8 for the recency cap (incl. prompt_chars bounding), 9 for the wikilink repair (phantom-row removal reproducing the live case, leaf-resolve, neutralise, idempotency), 1 end-to-end scholar-pipeline wiring test.

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