Programmatic session naming — hook-callable rename + Skill tool as hook target

+1 on this — my use case overlaps the first half (hook-callable rename) and adds a data point on why the obvious DIY workaround doesn't work.

Use case

SessionEnd hook that reads a pending title from ~/.claude/.rename-pending/<sid>.txt (written by some upstream process — backlog item id, commit subject, etc.) and applies it to the just-ended session.

What I tried

Since Claude Code itself writes {"type":"custom-title", ...} lines into the session JSONL during init / /rename, I wrote a hook that does the same. Two iterations:

1. Append at EOF — no sidebar update.
2. Replace the first existing custom-title line (or insert after line 1) via atomic temp-file + rename — still no sidebar update, even after desktop-app relaunch.

So the JSONL isn't authoritative for the sidebar. Corroborated by #37449 ("stat-log index not synced from JSONL") and #39228 (sessions with custom-title mid-file disappear from the panel — so the reader is position-sensitive and index-cached).

Concrete API suggestion

Matches the proposal in this issue. A SessionEnd (or new SessionRename) hook returning JSON on stdout:

{ "sessionTitle": "my custom title" }

The runtime would:

• Update the internal stat-log/index so the sidebar reflects it without app relaunch.
• Optionally also write the custom-title line to the JSONL for continuity with the existing on-disk format.

Stdin to the hook already carries session_id and transcript_path; returning a title on the same channel means no consumer has to reverse-engineer the index format (which is the thing that burned me — I never found where the sidebar actually reads from).

Scope note

Also relevant for #36379 (auto-titles override user renames) and #41378 (desktop app doesn't reflect title changes until reactivation) — a single authoritative write path from hooks would simplify the fix for all three.

human here - I just want the session names to reflect the work, not the first action ('check memory' or whatever)

+1 — adding a concrete use case from a different angle.

As a user with a "prefix session title with #<num> — whenever a GitHub issue is referenced" convention enforced via memory rules, I have no way to apply this automatically. The model "knows" the rule and can include it in chapter titles via mark_chapter, but the session title in the sidebar stays whatever was inferred from my first prompt — usually something like "Investigate failing test" instead of "#5484 — Investigate failing test".

Use cases beyond the original

• Issue-tracker prefix conventions (#1234 — ..., [ABC-42] ...)
• Project/tenant tags ([acme] ..., [vd] ... for multi-tenant work)
• Outcome-based renames at task close (already covered in #41888)

API preference

Of the options floated across #44786 / #40496 / #41888, the hook stdout JSON ({"sessionTitle": "..."}) is the most composable — it works from SessionStart, UserPromptSubmit, and SessionEnd uniformly, and doesn't require new tool plumbing. An MCP tool set_session_title would be a nice complement for in-conversation renames driven by the model itself.

Current workaround

Manual rename in the sidebar after each session — brittle and easy to forget. Tried writing custom-title lines into the JSONL (per this issue's investigation) — sidebar doesn't pick them up.

+1 with a Windows Desktop App data point — this confirms the override behaviour is cross-platform, not just CLI/IDE.

Setup

• Claude Code Desktop App (Windows 11), autoUpdatesChannel: "latest"
• User-global UserPromptSubmit hook in ~/.claude/settings.json calling a script that emits {"hookSpecificOutput":{"hookEventName":"UserPromptSubmit","sessionTitle":"YYYY.MM.DD MyProject"}}

Observed

1. Hook fires correctly on every prompt — confirmed via diagnostic log written by the script itself:

``
=== <date> <time> ===
CLAUDE_PROJECT_DIR=<project>/.claude/worktrees/<id>
title=2026.05.01 MyProject
``

1. JSON output is valid and matches the spec from the hooks doc.
2. UI session title nevertheless shows the LLM-generated auto-summary (e.g. Add tests for core functionality for a test prompt). Hook-supplied title is never visibly applied — even after Claude Code restart and full Windows reboot.
3. /rename not available in the Desktop App env (/rename isn't available in this environment.), so no in-app workaround.

Why this matters here

The fix proposed in this issue (authoritative hook stdout {"sessionTitle": "..."} write path that updates the index/sidebar without relaunch) would also resolve the silent override on Desktop App — the auto-titler currently wins the race against the hook output, leaving documented hookSpecificOutput.sessionTitle effectively non-functional for end users on Desktop.

Happy to share the full hook script + log if useful.

The workaround that I'm currently using:

A UserPromptSubmit hook (in ~/.claude/settings.json) runs a script that reads transcript_path from stdin, extracts your last assistant turn, and greps for a marker like <!--rename: TITLE -->, emitting {"hookSpecificOutput":{"hookEventName":"UserPromptSubmit","sessionTitle":"TITLE"}} — because only SessionStart/UserPromptSubmit (not Stop) can set the title, so the rename lands on your next message.

A CLAUDE.md rule instructs Claude to end replies with that marker when the session name is stale, so naming happens automatically with no /rename copy-pasting — just a one-message delay.