commit the provider list as soon as its own fetch settles, and say so while it loads

[atomantic]

Summary

The CoS Schedule page rendered a provider picker whose only option was "Default (active provider)" for seconds after load — a slow control that reads as a broken one.

Latency. /providers is a cache-only read that returns in milliseconds, but ChiefOfStaff.fetchData bundled it into a five-way Promise.all and committed the result only after the slowest sibling settled — and getCosActionableInsights runs a server-side PM2/memory health check plus a cross-repo git scan. Providers now commit on their own settle, mirroring the healthRead split four lines above.

• applyProviders is the single write path (as applyHealth is for health), so a future writer can't set providers without stamping the settle flag.
• A sameJsonShape guard keeps the array identity stable when the payload is unchanged — otherwise the earlier commit would cost a full-tree re-render on every 30s poll, since providers is an unmemoized prop down through every schedule card.

Empty-vs-unsettled. An empty providers array is ambiguous: "still fetching" and "none configured" both render a picker offering only the caller's emptyProviderOption. ProviderModelSelector gains a loading prop that disables its three selects and says "Loading providers…" instead — the same settle-gate it already applies to its own tool-use capability scan, now applied to the list the caller owns.

Wired through the Schedule tab: the card's quick pins and all three pickers in the task config drawer, so no picker sits enabled-but-empty beside a disabled one.

Follow-up

#6087 tracks the remaining pickers (Tasks/Agents/Workflow tabs, plus the ~15 that fetch through useProviderModels — which already returns a loading flag nobody reads) and the same head-of-line block still affecting getApps.

Test plan

• client suite: 10178 passed, 2 skipped, 0 failed
• npm run lint (biome): clean
• New coverage:
  • ProviderModelSelector.test.jsx — the loading option replaces the caller's sentinel, renders even when the caller forces a selection, disables the model select, and reverts once the list settles
  • AppTaskCard.test.jsx — the card actually threads the flag through to the picker