fix: model catalog follows the session's backend (web)

[saucam]

The bug you hit: switching a session's backend didn't refresh the model catalogue — the picker kept showing the previous backend's models.

Root cause (two compounding issues)

1. The web client never told the daemon which backend's models it wanted. fetchModels sent {type:"models.list"} with no provider field, so the daemon always answered for its default backend (claude), and the result was cached globally and never refetched. So every session — codex, pi, whatever — showed claude's models.
2. Backends report their models lazily (claude's #query, codex's #proc, pi's rpc all spawn on the first turn), so a never-used backend has an empty catalog until then. Combined with Memory/sqlite vec retrieval #1, a fresh codex session showed a stale claude list indefinitely — exactly the "never used codex on that machine" case.

Fix (client-side, targeted)

• fetchModels(provider?, force?) sends the backend on the wire and caches per-backend; the visible catalog tracks the requested backend, with a switch-race guard so a slow response for a backend you already navigated away from is dropped.
• Switching to an unfetched backend clears the previous list synchronously — the picker never flashes the wrong models.
• ModelPicker refetches (forced) whenever the focused session's providerId changes; the bare /model slash fetches the focused session's backend, not the daemon default.

A never-used backend still shows an empty catalog until its first turn (the models are genuinely unknown until the backend spawns) — honest, and the picker hides rather than lying. Once it runs once, re-opening the picker populates it.

Why not a daemon fix

listModels() returns empty for every provider until its backend spawns on the first turn — so a daemon "refresh on switch" would have to spawn the backend just to enumerate models, which we don't want. The daemon already caches + persists each backend's catalog after its first turn; the client just has to ask for the right one.

Follow-up worth considering: push a models update to attached clients when a backend first reports its catalog, so the picker auto-populates after the first turn without a manual re-open. Filed as a note, not blocking.

Tests

• models.test.ts (new, 7): provider sent on the wire, default when omitted, switch swaps the catalog, cached-live served without refetch, not-yet-live refetched, stale-list cleared synchronously on switch, slow-response-after-switch dropped.
• SessionControls.test.tsx (+2): picker fetches the session's backend on mount; refetches when providerId flips (the reported bug).
• Full web suite 206 green; tsc -b --noEmit clean.

The TUI (codeoid-ui) has the same class of bug (its models.list has no provider field at all) — fixed in a separate codeoid-ui PR.

🤖 Generated with Claude Code

[github-actions]

🤖 Gemini code review

This PR successfully resolves the issue where the model catalog failed to update when switching a session's backend. It implements per-backend model catalog caching, clears stale models synchronously upon switching to avoid flashing incorrect options, and adds robust unit tests.

Findings: 🔴 0 · 🟠 0 · 🟡 0 · 🟢 1

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_{Tokens spent · ⬆️ Input: 4,851 · ⬇️ Output: 256 · Σ Total: 11,338
Total may be higher due to thinking token counts.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.46%. Comparing base (f86384b) to head (589530c).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #160   +/-   ##
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  Coverage   84.46%   84.46%           
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  Files         104      104           
  Lines       18263    18263           
=======================================
  Hits        15426    15426           
  Misses       2837     2837           

Flag	Coverage Δ
daemon	84.46% <ø> (ø)

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