bug(managed-skills): provider declaring personalAgentSkills unsupported blocks every session spawn #1014

Expected

Registering a provider that declares personalAgentSkills: { supported: false } must not affect spawning sessions of OTHER providers. Managed-skill (TLDR/Goal/personal) health should be computed over providers that actually support personal agent skills.

Actual

After merging the grok integration (PR #844, main @ 5fda2f0), every session:spawn / session recovery fails in ~7ms with:

Error occurred in handler for 'session:spawn': Error: TLDR skill is unavailable or conflicts with an existing file. Review managed skill health in Settings.
    at out/main/index.js:71896

The renderer flattens this to "Session failed to start. Check provider setup and retry." All providers (claude/codex/opencode) are affected; no agent can start.

Root cause chain

1. src/providers/registry.main.ts:153 — grok is the first registered provider to declare personalAgentSkills.supported === false.
2. src/main/agentCodeConventions/targets.ts:64-67 — every registered provider with supported: false is pushed into unsupportedProviders (no install-gating; applies on every machine).
3. src/main/agentCodeConventions/AgentCodeConventionsService.ts:3036 — customHealth(): any unsupported provider ⇒ TLDR skill health = 'unsupported'.
4. AgentCodeConventionsService.ts:833 — ensureProductSkill() requires 'active' and throws otherwise.
5. Pre-spawn reconcile (src/main/sessionManager.ts:2618) runs ensureTldrSkill() before every spawn, for every provider.

Latent design flaw exposed: the managed-skils layer assumed "all registered providers support personal skills". Grok is the legitimate first counter-example.

Secondary breakage from the same assumption: the unsupportedProviders.length > 0 gates at AgentCodeConventionsService.ts lines 1145/1400/1518/1807/2030/2159 also block enabling any personal/custom skill app-wide.

Evidence

Incident journal run 2026-09-19T04-09-36-635Z-main-23681-9e113a:

• 15× conventions.pre_spawn_reconcile.error (all "TLDR skill is unavailable...")
• 15× recover.failed with code: start-failed, durationMs ~7 (fails before any CLI launch), kinds: claude/opencode/codex

Why tests missed it

Every conventions test stubs resolveTargets with unsupportedProviders: []; no integration test boots the real registry together with the conventions service.

Fix direction

Compute product-skill health over supported targets only. Unsupported providers surface as informational per-provider rows in Settings (the customUnsupportedStatuses() mechanism) but do not block spawns or skill enablement. Keep 'unsupported' health only for the degenerate case of zero supported providers.

Environment

• main @ 5fda2f0 (post PR feat(grok): build native provider integration #844 merge), dev run, macOS
• Reproduces deterministically on every spawn attempt