The usePromptActions hook is the textbook "god hook" AGENTS.md warns against.
As a first, safe slice, pull its module-level standalone helpers (no closure
over hook state) into a focused, testable use-prompt-actions-utils.ts sibling:
- error classifiers: isSessionNotFoundError, isSessionBusyError,
isProviderSetupError, inlineErrorMessage
- session-busy retry: withSessionBusyRetry (+ its constants)
- attachment IO: base64FromDataUrl, imageFilenameFromPath,
readImageForRemoteAttach, readFileDataUrlForAttach, friendlyRemoteAttachError
- misc: delay, isSessionIdCandidate, blobToDataUrl, renderCommandsCatalog,
slashStatusText, appendText, visibleUserOrdinal, visibleUserIndexAtOrdinal,
the _submitInFlight guard set, and the GatewayRequest type
Pure restructuring, no behavior change; the usePromptActions and
uploadComposerAttachment exports (and their import paths) are unchanged. Adds
unit tests for the pure helpers. use-prompt-actions.ts: 1,956 -> 1,772.
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