fix(workflow): a failed host call on the plugin Settings page is silent (state, save, set-model) #1504

Written-by: FlyBot Lead
Owner: Dev2
Base: fe6c90693f5ff32c1147d0b618041b1acaaa0d76

The plugin-registered Settings → Workflow graphs page (plugins/workflow/client.js, WorkflowSettings) treats a failed host call as if it never happened: no alert, no retry, and in two of the three cases the page keeps claiming the opposite of the truth.

What happens (all three on current main)

1. workflow/state read fails — the page stays on Reading workflows… forever. No error text, no retry; the rejection surfaces only as an unhandledRejection: The workflow host did not answer.
2. workflow/graph save fails — the call rejects, nothing is shown, and while editing the page still says Changes are saved automatically.
3. workflow/set-model fails (the picker added by #1503) — the select shows the new model, no error, so the user believes the switch was saved.

Cause is the same shape in all three: the call site has a .then and no .catch, and both setLoading(false) and setError(...) live inside the then. call() in core/src/client/api.js throws on a network error, on !response.ok, and on result.ok === false (except REFUSALS), so the failure path never runs and the value?.ok === false branches in these handlers are dead code.

Reproduction

plugins/workflow/test/client.test.js already renders the page through the hook renderer. Make the injected call reject for the endpoint under test, then read what the page shows:

• workflow/state: CALLS = ['workflow/state'], ALERTS = 0, text contains Reading workflows… = true, unhandled rejections = 1 (The workflow host did not answer).
• workflow/graph (rejection path; the {ok:false} path already reaches the alert on main): ALERTS = 0, text contains Changes are saved automatically = true, unhandled rejections = 1.
• workflow/set-model: ALERTS = 0, unhandled rejections = 1 (The model switch failed).

Expected

• Each failure ends the load, lands in the page's existing .wf-err line (role="alert") with the failure's own message, and leaves no unhandled rejection.
• The read failure offers a retry, and retrying re-reads workflow/state and renders the graph.
• A failed save does not render Changes are saved automatically; the next successful save clears the alert and the hint returns.
• Success paths stay byte-for-byte as they are today.

Scope

• plugins/workflow/client.js: one shared settled-call helper (throw / reject / no answer within a timeout all become one error string) wired into the three sites above; the read additionally gets the retry.
• plugins/workflow/test/client.test.js: four tests, one per failure plus the never-answering host.
• docs/subsystems/workflow.md: one line (arch-docs owns plugins/workflow/ through that page).
• No new endpoint, no schema, permission or credential change.
• core/src/client/workflows.js and the core Settings page are not touched: that page already settles a failed read through readWorkflows() into an error row with a retry. This issue is the plugin page only.
• patches/ds-bot/* and core/client.js do not change: the plugin client is not part of the client bundle (no wf-settings-canvas in core/client.js).

Acceptance

• The four new tests fail on fe6c9069 with the product code reverted and pass with the fix (89 tests, 85 pass / 4 fail → 89/89).
• TZ=UTC npm run verify exits 0; node scripts/ds-bot-patches.mjs check reports its three ok lines; node core/scripts/build-client.mjs --check exits 0.

Related, not duplicates

• #1480 is No workflows yet on a page that did load (handled by #1490).
• #1458 is the same family of "a failure shown as an empty board" but on the Assign dialog; it is frozen and this page is not fixed by it.