Bound agent skill catalogs and add deterministic discovery filters

[LadyBluenotes]

Problem

Skill bodies load on demand, but discovery context grows with every permitted skill. Hooks emit all identifiers and descriptions, and list output offers no result budget or package/path filtering.

Evidence

With one short skill per synthetic package, compact identifier/description catalogs measured 1,009 bytes for 10 skills, 10,279 for 100, and 52,279 for 500. The hook maps over all skills; its session-start matcher includes startup, resume, clear, and compact. Live agent reinjection behavior and actual token counts were not measured.

Sources: list output, hook catalog, existing eval harness.

Verified against main at 206e987 (@tanstack/intent 0.3.8), Node v24.12.0 on macOS arm64. Tests used installed dependencies and synthetic local fixtures.

Acceptance criteria

• Define a deterministic package/path filtering or search surface using existing identifiers and metadata.
• Agent catalog output has an explicit byte/character budget, visible omitted-result count, and a way to retrieve remaining results.
• Policy filtering and hidden-source redaction apply before results are exposed.
• Loaded instruction bodies remain complete; catalog limits do not silently truncate instructions.
• Tests cover 10, 100, and 500-skill catalogs, deterministic ordering, overflow, and no-match cases.
• Extend the existing eval harness to record context bytes, correct selection, and unnecessary loads without equating smaller output with better task quality.

Scope and priority

Priority: High. Type: feature.

Follow-up release; not a v0.4.0 blocker. Coordinate diagnostics with #222. No embeddings, vector database, daemon, or new evaluator.