[shivaam]

When the API refuses an action, the error toast showed only the HTTP status text. createErrorToaster used error.message, which for an ApiError is the status text, so deleting a running Dag run toasted "Error deleting Dag Run / Conflict" while the response said why:

	Toast
Before	Error deleting Dag Run — Conflict
After	Error deleting Dag Run — The DagRun with dag_id: `example` and run_id: `manual__…` cannot be deleted in running state

The toaster now uses the response detail when there is one, through the existing getApiErrorDetail (already used by ErrorAlert), and keeps error.message as the fallback. Every action that goes through the shared toaster (delete, clear, patch, trigger, pause, …) benefits. 403s are still left to the MutationCache handler.

Two hooks had worked around this on their own, and now use the shared helper:

• useUpdateHITLDetail special-cased exactly this in Refuse Human-in-the-loop responses once the task stopped waiting #75645. Its test expected the bare response.error title key only on that branch; the shared helper translates the namespaced hitl:response.error, which renders the same text.
• useClearTaskInstances showed the detail only when it contained "AirflowClearRunningTaskException", so other refusals such as "Cannot clear running task instances" still showed "Conflict".

On what gets shown: the text is rendered as a React text node, so no markup is interpreted. It is the same detail the browser already received and that ErrorAlert already displays. Database and Dag deserialization errors keep the statement redacted unless [api] expose_stacktrace is on, and validation errors show only loc and msg, never the submitted input.

Testing:

• New errorHandling.test.ts, plus a clear-task test; both fail against the old code.
• Full UI vitest suite, eslint, prettier, tsc, and prek (pre-commit and manual stages).
• Manually in a local Airflow: deleting a running Dag run shows "Conflict" before and the reason after; clearing a running task with "Prevent rerun if task is running" still shows its reason.
  Before

After

---

Was generative AI tooling used to co-author this PR?

• Yes — Claude Code (Opus 5.5)

Generated-by: Claude Code (Opus 5.5) following the guidelines