refactor(server): make title prompts plaintext

[t3dotgg]

The initial and regeneration title prompts became difficult to read and tune after being assembled from conditional arrays.

This makes both prompts explicit plaintext templates, leaves a reminder to keep their shared editorial rules aligned, and reduces the shared message builder to the branch-name behavior it actually supports. Generated prompt content and runtime behavior are unchanged.

Testing

• vp test run apps/server/src/textGeneration/TextGenerationPrompts.test.ts (19 tests passed)
• vp fmt apps/server/src/textGeneration/TextGenerationPrompts.ts --write
• git diff --check

The server-wide local typecheck remains blocked by existing Effect and dependency diagnostics in unrelated files; the changed file reports no diagnostic.

Made with GPT-5.6 Sol (low reasoning) through the Codex harness in T3 Code.

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Note

Low Risk
Prompt-only refactor with existing tests passing; no API or provider wiring changes beyond how strings are assembled.

Overview
Thread title generation no longer builds prompts from nested conditional arrays via buildPromptFromMessage. Initial and regeneration flows now use dedicated plaintext templates (INITIAL_THREAD_TITLE_PROMPT, regenerateThreadTitlePrompt), with a comment to keep shared editorial rules aligned between them.

The shared buildPromptFromMessage helper is trimmed to what branch-name generation still needs: fixed "Rules:" / "User message:" labels and no optional guidance, custom rule labels, or tail sections. preserveMessageEnd and attachment/policy suffix assembly move to thread-title-only helpers (threadTitlePromptSuffix, direct string composition in buildThreadTitlePrompt).

Intended prompt text and runtime behavior stay the same; this is structure and readability for tuning titles.

^{Reviewed by Cursor Bugbot for commit 4ef544f. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Rewrite thread title prompts as plaintext in buildThreadTitlePrompt

• Replaces the generic buildPromptFromMessage-based title prompts with dedicated plaintext prompt strings for initial and regeneration modes.
• Adds INITIAL_THREAD_TITLE_PROMPT (fixed editorial instructions) and regenerateThreadTitlePrompt (references the previous title with structured guidance) in TextGenerationPrompts.ts.
• Regeneration mode now uses tail-preserving truncation via preserveMessageEnd so the most recent content is retained; initial mode uses start-based truncation via limitSection.
• Strips guidance, rulesLabel, afterRules, messageLabel, and preserveMessageEnd from PromptFromMessageInput, making buildPromptFromMessage always emit fixed Rules: and User message: labels.
• Behavioral Change: title prompts now differ substantially from other prompts — regeneration includes a truncation marker for long threads, and callers can no longer customize labels or guidance sections.

^{Macroscope summarized 4ef544f.}

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[macroscopeapp]

Approvability

Verdict: Approved 4ef544f

This is a straightforward refactor that converts dynamically-built title prompts into static plaintext constants for improved readability. The prompt content is preserved unchanged, and no runtime behavior is affected.

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