Web Shell Prompt Send Failure Retry

Goal

Make a prompt transport failure visible on the user message that failed to send, and let the user retry it without creating a duplicate message.

Behavior

• Only failures before daemon admission are shown as send failures. Errors after admission continue to use the existing turn-error retry UI.
• The failed user message shows an inline "Failed to send" label and a retry icon directly below its bubble.
• Retrying sends the original text, images, and input annotations without appending another optimistic user message.
• The failure indicator is removed as soon as the retry starts.
• The global processing indicator stays hidden until the daemon admits the retry, then starts timing from the retry attempt rather than the original failed message.
• If an admitted retry later becomes a turn error, retrying from the existing turn-error UI also starts a new timer for that retry attempt.
• If the retry also fails before admission, the indicator returns.
• As soon as a newer user message is sent, the previous message no longer offers retry.
• Session changes or transcript reconciliation remove failure state whose message is no longer present.
• The first prompt in a lazily created session uses the allocated session ID even before the connection render catches up.

Scope

The state remains local to the Web Shell UI and is keyed by both the owning session and the exact optimistic user message ID captured when it is appended. Failures settling after a session change are ignored. The daemon transcript schema and SDK store remain unchanged.