fix(desktop): disabling a provider's last model no longer re-enables all toggles

[xxxigm]

Summary

In the desktop Models visibility dialog, disabling the last enabled model of a provider (e.g. the final Anthropic model) made every toggle for that provider snap back on. As reported, this happens for any provider — emptying one resets it to all-visible.

Root cause

effectiveVisibleKeys re-seeds a provider's curated defaults whenever the stored visible-set has zero keys for that provider:

const hasStoredProvider = [...stored].some(key => key.startsWith(providerPrefix))
if (hasStoredProvider) continue
// ...seed this provider's default models...

That heuristic exists for a good reason — to surface a genuinely new provider by default after an update adds it. But it can't tell a new provider apart from one the user intentionally emptied: both look like "zero stored keys." So hiding a provider's last model drops it to zero keys → next render re-seeds all of its defaults → every toggle flips back on.

Fix

Track the providers the user has already customized in a new $knownProviders set (persisted alongside the visible set, unioned so a partial/transient provider list never drops a slug). effectiveVisibleKeys now seeds a zero-key provider's defaults only when it is not known:

• Known provider with zero visible keys → user deliberately hid everything → stays empty (the bug).
• New provider absent from the known set → still seeded visible (feature preserved).

The dialog and the status-bar model menu both pass the known set through; the toggle handler records the on-screen providers as known on every customization.

Test plan

apps/desktop/src/store/model-visibility.test.ts (run via repo-root vitest):

• Existing: new provider with stale stored choices stays visible.
• Existing: a provider with stored choices isn't re-seeded.
• New: a known provider whose last model was hidden stays empty (no snap-back).
• New: a brand-new provider absent from the known set is still seeded visible.
• New: setVisibleModels unions known provider slugs across customizations.

vitest run --config apps/desktop/vite.config.ts apps/desktop/src/store/model-visibility.test.ts
# Test Files 1 passed (1) — Tests 5 passed (5)
tsc --noEmit -p apps/desktop/tsconfig.json   # 0 errors

[alt-glitch]

Duplicate of #43496 (same root cause/fix for #43485 — distinguish a user-emptied provider from a genuinely new one). #43496 is the earlier open canonical; #43492/#43542 already closed as dupes of it. Non-core desktop UX.

[kshitijk4poor]

Closing as superseded by #50100 (merged: commit 8ca38d3), which fixes the same cross-provider model-visibility snap-back. This PR targets the pre-#43496 code and takes a heavier approach (a new $knownProviders store plus signature changes to effectiveVisibleKeys/setVisibleModels); the merged fix builds on the #43496 sentinel design with a smaller, contained change. Thanks for the report and the effort on this bug class.