## Summary
Simplifies the error overlay so it presents one clear title, one clear
message, and one stable details action instead of rendering a list of
per-error messages.
## Changes
- **What**: Extracts the error overlay view model into
`useErrorOverlayState`, adds focused unit coverage for the overlay copy
resolution rules, and updates the overlay E2E coverage to match the new
behavior.
- **Breaking**: None.
- **Dependencies**: None.
### Behavior changes
- The overlay body no longer renders a `<ul>` of individual error
messages. It now always renders a single paragraph message.
- Single-error overlays now prefer toast-specific copy when it exists.
For execution errors, the overlay resolves the message in this order:
`toastMessage`, `displayMessage`, raw `message`, group `displayMessage`,
then group `displayTitle`. The title resolves from `toastTitle`, then
`displayTitle`, then the group title.
- Single non-execution groups use group-level toast/display copy. This
lets grouped error types supply overlay-friendly copy without the
overlay needing to understand each card implementation.
- Multiple-error overlays now ignore individual error item copy in the
overlay itself. The header becomes the pluralized count title, for
example `7 errors found`, and the body becomes the fixed guidance
message: `Resolve them before running the workflow.`
- The overlay is hidden if the store reports an error count but no
resolved overlay message exists. This avoids rendering a visible shell
with an empty body.
- The action button no longer varies by error type in normal app mode.
Missing nodes, missing models, missing media, swap nodes, validation
errors, and runtime errors all use `View details` instead of labels like
`Show missing nodes`, `Show missing models`, `Show missing inputs`, or
`See Errors`.
- App mode keeps its existing `Show errors in graph` action label.
- The overlay width now keeps the previous width as its minimum and
allows a wider maximum, reducing avoidable wrapping in longer error
headers.
- The live region was softened from an assertive alert-style
announcement to `role="status"` with `aria-live="polite"` so updates
such as count changes are less disruptive.
### Tests
- Adds component coverage for the rendered overlay shape and app-mode
action label.
- Adds composable coverage for single execution errors, runtime errors,
grouped missing media errors, multiple-error aggregate copy, hidden
empty-message state, and display-copy fallback behavior.
- Updates `errorOverlay.spec.ts` so the E2E suite checks the new
single-message overlay, the stable `View details` action, and the fixed
multiple-error body guidance.
- Removes the old type-specific button-label E2E expectations because
that branch no longer exists in product behavior.
### Follow-up PR
A follow-up PR is stacked on top of this one:
`jaeone/fe-816-missing-resource-error-messaging`.
That follow-up will wire missing resource error resolvers into the copy
model consumed here. It covers missing node packs, missing models,
missing media, and swap-node groups, including the group-level
`toastTitle`, `toastMessage`, `displayMessage`, `displayDetails`, and
item label copy those cards need. This PR intentionally keeps the
overlay behavior separate so it can merge first without depending on the
missing-resource resolver copy.
## Review Focus
- Please check the single-error versus multiple-error overlay behavior,
especially the fallback order for execution error copy.
- Please check that the `View details` action is now intentionally
error-type agnostic in normal app mode while app mode keeps `Show errors
in graph`.
- Please check the empty-message guard and the requirement that a
single-error overlay only resolves a single group when the total error
count and group list agree.
- Please check the E2E reduction: the old type-specific action-label
assertions were removed because the UI branch they tested was removed.
## Screenshots (if applicable)
N/A
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