Fix focus stolen from terminal when commit message prefix is updated

[thomasrepnik]

Summary

When the branch changes (e.g. git checkout in the IntelliJ terminal), the plugin updates the commit message prefix — but it also stole keyboard focus from the terminal and moved it into the commit message field.

Root cause (verified against IntelliJ 2023.2.4 sources): the plugin called CheckinProjectPanel.setCommitMessage(...), and the platform's CommitProjectPanelAdapter implements that as setText(...) followed by commitMessageUi.focus() — in both the non-modal commit tool window and the modal commit dialog. The write also happened unconditionally on every GIT_REPO_CHANGE event (fetch, ticket-less branches), stealing focus even when nothing changed.

Fix (only CommitPrefixCheckinHandler.java):

• New pure static calculateNewCommitMessage(...) returning Optional.empty() when the branch has no ticket or the computed message is unchanged (compared right-trimmed, since CommitMessage.getText() trims trailing whitespace). No-op repo events now do nothing at all.
• New setCommitMessageWithoutFocus(...): finds the CommitMessage component via UIUtil.findComponentOfType(panel.getComponent(), ...) and calls its setCommitMessage(...), which only sets text and never requests focus. Falls back to panel.setCommitMessage(...) for unknown panel implementations.

All prefix/ticket logic (updatePrefix, getTicket, settings, listener wiring) is untouched. Manually verified: prefix still updates on terminal checkout, focus stays in the terminal.

Note: bypassing the adapter also skips its VcsConfiguration.saveCommitMessage(oldText) call, so intermediate prefix rewrites no longer pollute the "recent commit messages" history; the final message is still saved on commit.

Test Coverage

10 new parameterized tests for calculateNewCommitMessage (TDD: written first, confirmed failing, then implemented). Tests: 133 → 143 (+10 new), all passing.

calculateNewCommitMessage(ticketSystem, branchName, currentMessage, wrapL, wrapR, pos)
 +-- no ticket in branch --> empty                    [TESTED]
 +-- ticket, message unchanged (incl. rTrim) --> empty [TESTED: START/END, JIRA/OTHER]
 +-- ticket, message changed --> new message           [TESTED: null current, START/END, JIRA/OTHER]

UI layer (no platform test fixtures in project):
 setCommitMessageWithoutFocus / updateCommitMessage    [manually verified in IDE]

Coverage audit: 9/11 testable paths (82%). Remaining gaps are low-risk Optional-plumbing combinations (OTHER system with no-digit branch; blank-but-non-null current message) whose underlying logic is covered by existing getTicket/updatePrefix tests.

Pre-Landing Review

• Adversarial review recommendation: land it. Confirmed the fix mechanism is correct for both stock commit UIs and the rTrim guard is required (prevents rewrite-per-event caret jumps) and loop-free.
• Informational: two cases in calculateNewCommitMessage_messageUnchanged_returnsEmpty (main/develop) exercise the no-ticket branch rather than message equality — cosmetic naming only.
• Pre-existing issues noted for future work (not introduced or worsened here): message-bus connection is never disposed (stale handler leak), repositoryChanged ignores its repository argument in multi-root projects.

Test plan

• ./gradlew test — 143/143 pass (fresh run on merged state)
• ./gradlew buildPlugin — builds successfully
• Manual: git checkout <ticket-branch> in the IDE terminal updates the prefix without stealing focus

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