Up-arrow prompt history is shared across concurrent Claude Code tabs in the same directory

Summary

Running multiple Claude Code instances in separate terminal tabs (same working directory) causes them to share the same up-arrow prompt history. Pressing Up in tab A surfaces prompts I typed in tab B, and vice versa.

Related to (but not exactly the same as) #15631 — that issue asks for per-session scoping; this one focuses on the concurrent-tab UX, which is the most common multi-session scenario for me.

Repro

1. Open terminal tab A in ~/some-project, run claude
2. Open terminal tab B in ~/some-project, run claude (separate session)
3. Type a prompt in tab A, submit
4. Switch to tab B, press Up arrow
5. Observed: the prompt from tab A appears in tab B's input
6. Expected: each tab's up-arrow recalls only that tab's prompts (or at least gives me a setting to opt into that)

Root cause (from inspection)

~/.claude/history.jsonl is a single global file. Each line records project (cwd) and sessionId. Up-arrow appears to filter by project only — not by sessionId or PID — so all concurrent instances in the same directory share the recall pool.

Example entries already include the session ID; the data needed for per-session filtering is right there:

{"display":"...","project":"/path/to/repo","sessionId":"a9bb95e1-..."}

Why it matters

• I keep multiple Claude tabs open for parallel work in the same repo (one debugging, one refactoring, one writing tests). Their prompt histories should not bleed across.
• Up-arrow becomes noisy: I scroll past prompts I never typed in this tab.
• Privacy/safety smell: a forked or shared terminal can surface prompts from a sibling session.

Requested fix

Either:

• (A) Filter up-arrow history by sessionId by default, OR
• (B) Add a setting:

``json
// ~/.claude/settings.json
{ "commandHistoryScope": "session" } // values: "session" | "directory" (current) | "global"
``

/clear should continue to behave as today regardless of the setting.

Environment

• Claude Code: 2.1.139
• Platform: macOS (Darwin 24.5.0)
• Shell: zsh
• Terminal: multiple concurrent tabs

References

• #15631 (open) — per-session history scoping
• #32400 (closed, stale) — same ask
• #7702, #15630, #20064 — older duplicates