fix(chat): honor [skills] enabled=false at runtime

[penso]

Summary

Closes #655.

SkillsConfig.enabled is documented and defaulted to true in the schema (crates/config/src/schema.rs:1275), but the runtime never consulted it — FsSkillDiscoverer::default_paths() was invoked unconditionally from every chat.rs callsite, so every discovered SKILL.md landed in the system prompt regardless of [skills] enabled = false. This is the same failure mode as #638 / #639: schema promises behavior the code doesn't deliver.

• Added discover_skills_if_enabled(&MoltisConfig) helper in crates/chat/src/lib.rs that returns Vec::new() when config.skills.enabled is false, otherwise delegates to FsSkillDiscoverer.
• Routed all four FsSkillDiscoverer usages inside LiveChatService (send path, model-probe path, and the two load_prompt_persona_for_session paths) through the helper. The first two thread a fresh moltis_config::discover_and_load() (matching surrounding patterns); the other two reuse the already-loaded persona.config.

Non-chat callsites (cli, gateway/services, gateway/server, skills/watcher, tools/skill_tools, httpd/server) are intentionally out of scope — they don't inject skills into the LLM prompt. Can be a follow-up if full coverage is desired.

Validation

Completed

• cargo check -p moltis-chat
• cargo +nightly-2025-11-30 fmt --all -- --check
• cargo +nightly-2025-11-30 clippy -p moltis-chat -p moltis-config -p moltis-skills --all-targets -- -D warnings
• cargo test -p moltis-chat --lib → 175 passed, 0 failed (includes two new regression tests)

Remaining

• just lint (full Darwin clippy sweep)
• just test (full test suite)
• ./scripts/local-validate.sh <PR>

Manual QA

1. Add to moltis.toml:

   [skills]
   enabled = false

2. Place a SKILL.md under <data_dir>/skills/test-skill/SKILL.md.
3. Start a session and inspect the system prompt / <available_skills> block.
4. Expected: no skills discovered, no <available_skills> entries. Flip enabled = true and confirm the skill reappears.

Tests

Two new #[tokio::test]s in crates/chat/src/lib.rs:

• discover_skills_if_enabled_short_circuits_when_disabled — plants a real SKILL.md under a temp data_dir and asserts the helper returns an empty list when enabled = false, proving we don't fall through to the filesystem.
• discover_skills_if_enabled_runs_discoverer_when_enabled — the complementary arm, asserting the planted skill is discovered when enabled = true.

Tests share a module-local tokio::sync::Mutex so they serialize their mutations to the global moltis_config::set_data_dir override.

[greptile-apps]

Greptile Summary

This PR fixes #655 by adding a discover_skills_if_enabled async helper that returns an empty vec when config.skills.enabled is false, and routes all four FsSkillDiscoverer call sites in LiveChatService (send path, model-probe path, two persona paths) through it. Previous review feedback on Mutex<()> (replaced with Semaphore::const_new(1)) and the redundant discover_and_load() on the model-probe path have both been addressed in follow-up commits.

Confidence Score: 5/5

Safe to merge — the fix is correct, both code arms are tested, and prior review concerns are resolved.

All four callsites correctly route through the new helper; the semaphore replaces the forbidden Mutex<()>; the redundant discover_and_load() in the model-probe path was cleaned up in the final commit. No P0/P1 issues remain.

No files require special attention.

Important Files Changed

Filename	Overview
crates/chat/src/lib.rs	Adds discover_skills_if_enabled helper that gates skill discovery on config.skills.enabled, routes all four FsSkillDiscoverer call sites through it, and adds two regression tests using Semaphore::const_new(1) for proper test serialization.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[chat request arrives] --> B{send / model-probe / persona path}
    B --> C[call discover_skills_if_enabled\n&config]
    C --> D{config.skills.enabled?}
    D -- false --> E[return Vec::new\nno skills injected into prompt]
    D -- true --> F[FsSkillDiscoverer::default_paths\nmoltis_config::data_dir]
    F --> G[FsSkillDiscoverer::discover]
    G --> H{discover result}
    H -- Ok --> I[return Vec of SkillMetadata]
    H -- Err --> J[warn! + return Vec::new]
    I --> K[inject into system prompt\navailable_skills block]
    E --> L[skip available_skills block]

Loading

_{Reviews (3): Last reviewed commit: "fix(chat): reuse existing config in cont..." | Re-trigger Greptile}

[codspeed-hq]

Merging this PR will not alter performance

✅ 39 untouched benchmarks
⏩ 5 skipped benchmarks¹

---

_{Comparing precious-tibia (69a6141) with main (5afb1bc)}

Footnotes

1. 5 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[codecov]

Codecov Report

❌ Patch coverage is 82.08955% with 12 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/chat/src/lib.rs	82.08%	12 Missing ⚠️

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