Make Commit button failures more diagnosable

[tekumara]

Problem or use case

An agent can create a commit in a worktree, but clicking the Commit button for that worktree fails. The only error shown is:

Git command failed in GitVcsDriver.commit.commit (<worktree>): Git command exited with a non-zero status.

I do not know what Git rejected, or whether the button and the agent are using different staging, identity, environment, or hook behavior. The agent can commit successfully, but the button error gives me no way to diagnose the difference. I am not claiming a specific underlying Git failure; the request is for enough information to identify it.

Proposed behavior

Show an actionable reason when the failure is recognized (for example, a rejected hook and exit code or missing Git identity). For other failures, provide a details view or copyable diagnostic with enough context to identify the cause. If the button and agent use different commit contexts, make the relevant difference visible. Keep tokens, credentials, and credential-bearing URLs out of user-visible diagnostics.

Smallest useful scope

The UI Commit action: improve its failure message or diagnostic details without changing how agent-initiated shell commits work.

Current workaround

Ask the agent to commit, which succeeds, but leaves the button failure unexplained.

Related

Issue #4380 covers opaque Git errors generally; PR #8645 added safe reason classification but unknown failures remain generic. PR #7706 describes a commit-hook failure with the same generic message, and PR #21662 covers missing Git identity.