Sidebar: wrap thread titles at narrow widths, preserve child model tags, and wire up threadTitleInstructions

[cornishandy]

Problem

When running T3 Code (0.1.1-nightly.20261018.3302, commit d0918f1659f4) side-by-side with an editor or browser on a laptop screen, the thread sidebar has three friction points that work against a narrow layout:

1. Sidebar width is clamped at 208px minimum and every thread title uses single-line truncate.

   • In the web client (apps/web), the sidebar width clamp floors at 208px (default 256px), and thread titles across card rows, slim rows, draft rows, search results, and legacy project trees apply Tailwind's truncate (white-space: nowrap; overflow: hidden; text-overflow: ellipsis) alongside fixed row heights (h-[4.875rem] on cards, h-9 on slim rows).
   • Even at 208px, only ~20–24 characters of a thread title are visible before ... cuts off the distinguishing words at the end of the title.

2. Generated and child/subagent title limits don't match narrow-sidebar budgets (and cut off trailing model badges).

   • In packages/provider-core/src/server/textGenerationPrompts.ts, INITIAL_THREAD_TITLE_PROMPT and regenerateThreadTitlePrompt ask for 3-8 words, fewer than 40 characters, but sanitizeThreadTitle in packages/provider-core/src/server/textGeneration.ts sets MAX_THREAD_TITLE_CHARS = 120 and slices with raw UTF-16 .slice(0, 117) (which can also split surrogate pairs).
   • For delegated/subagent rows, subagentThreadTitle (packages/provider-core/src/server/subagentProjection.ts) slices at 72 chars (detail.slice(0, 69) + "...") and MCP's threadTitle (apps/server/src/mcp/toolkits/orchestrator/shared.ts) slices at 80 chars. When an orchestrator names a delegated review or build with the model/effort at the end—e.g. Final Review Gate: Verify OAuth PKCE callback, token refresh, and session expiry (Model xhigh) (94 chars)—both the 72-char and 80-char slices cut off the trailing (Model xhigh) badge while keeping the verbose middle description.

3. threadTitleInstructions exists in textGenerationPrompts.ts but isn't wired up.

   • threadTitlePromptSuffix(input) in packages/provider-core/src/server/textGenerationPrompts.ts already reads policyInstruction(input.policy?.threadTitleInstructions).
   • However, fromRunner(...).generateThreadTitle (packages/provider-core/src/server/textGenerationOperations.ts) and ThreadTitleRegenerationService (apps/server/src/orchestration-v2/ThreadTitleRegenerationService.ts) don't forward policy, and ServerSettings exposes branchNameInstructions, reviewGuideInstructions, and sourceControlWritingStyle.customInstructions, but no threadTitleInstructions.

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Proposal

1. Allow multi-line wrapped thread titles in the sidebar and a narrower optional minimum width (e.g. 140px while still respecting the measured titlebar button cluster).

   • Replacing truncate + fixed row height (h-[4.875rem] / h-9) with min-h-[4.875rem] h-auto (cards) and min-h-9 h-auto py-1.5 (slim rows) + overflow-wrap: anywhere lets titles wrap cleanly onto multiple lines, with rows expanding to fit in a narrow 140px–190px sidebar.

2. Word-boundary, Unicode-safe truncation and tag-preserving compaction for child/subagent titles.

   • In sanitizeThreadTitle, tighten the fallback ceiling to match the prompt budget (e.g. 40 characters, with a 36-character prompt target) and trim at a word boundary (using code-point/grapheme iteration rather than raw UTF-16 .slice() so surrogate pairs are never split).
   • In subagentThreadTitle and MCP threadTitle, if a child title ends with a short parenthetical badge like (GPT-6.1-Sol) or (Claude Opus 5.5), preserve the trailing (...) suffix, compact verbose Role: Subject prefixes when needed so the subject after : stays distinct, and word-trim before the badge (e.g. Review: OAuth PKCE... (GPT-6.1-Sol)).

3. Wire threadTitleInstructions through ServerSettings -> ThreadTitleRegenerationService -> fromRunner(...).generateThreadTitle -> buildThreadTitlePrompt.

   • Since threadTitlePromptSuffix already supports input.policy?.threadTitleInstructions, exposing a Thread title instructions field in Settings (next to the Text generation model selector or alongside branchNameInstructions / reviewGuideInstructions) would let users specify their own naming style (e.g. telegraphic noun phrases, <28 chars, Scope: Topic prefixes, or casing rules).

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What I'm running locally

On 0.1.1-nightly.20261018.3302 (d0918f1659f4), I patched my local app.asar (main-*.js, main-*.css, _chat-*.js, and binCli-*.mjs) to remove truncate on sidebar row titles, switch card/slim rows to min-height + height: auto, lower the sidebar width floor from 208 to 140 (while keeping Math.max(140, Math.ceil(e)) for the titlebar measurement), tighten the title prompt to 2-5 words, fewer than 36 characters with a 40-char word-boundary sanitizer, and compact subagent/child titles to <= 42 chars while preserving trailing (Model) tags and distinct subjects. In a ~160px sidebar, wrapped rows expand cleanly to fit without single-line text-overflow: ellipsis clipping.