fix(desktop): read tmux format output with a separator no tmux version escapes

[waleedlatif1]

Summary

• Sim joins the fields of tmux -F output with a 0x1f byte and splits on it. tmux 3.4 and 3.5 print control characters in format output as octal escapes, so the separator arrived as the four characters \037 and no line split.
• Effect on those versions:
  • Sim never found the tmux client running in a terminal, so it treated that terminal as a plain shell, and the agent's runs were refused as busy.
  • The panes operation came back empty.
• The separator is now the printable |~sim~|, which no tmux version escapes. A field that happens to contain it changes the line's field count, so that line is dropped rather than misread.

Why not accept both forms

• tmux 3.3 and later also escape backslashes (\ prints as \\).
• So "split on the byte or on \037" could cut a field whose text holds a real \037.
• Telling the cases apart would mean decoding each version's escaping. A printable separator doesn't depend on escaping at all.

Versions checked (real binaries)

tmux	0x1f separator	|~sim~| separator
2.9a	raw	verbatim
3.3a	raw	verbatim
3.4 (Ubuntu 24.04)	escaped as \037	verbatim
3.5a	escaped as \037	verbatim
3.6a	raw	verbatim
3.7c (current Homebrew)	raw	verbatim

On real tmux 3.4, listPanes returned nothing with staging's code and the session's panes with this change.

Autopsy

• The unit tests run against a fake tmux that printed format output unescaped, so this kind of bug could never fail them.
• The fake now escapes its output the way 3.4 and 3.5 do: backslashes doubled, control characters as octal escapes.
• The new attachment test goes through that fake. It fails with the old separator and passes with this one.
• It was found by a new Electron E2E against real tmux 3.4. That E2E follows in a separate PR.

Type of Change

• Bug fix

Testing

• Unit tests, red first with the old separator.
• Real tmux 2.9a, 3.3a, 3.4, 3.5a, 3.6a and 3.7c.
• Electron E2E with real tmux 3.4.

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

[waleedlatif1]

@greptile

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1 Skipped Deployment

Project	Deployment	Actions	Updated
docs	Skipped		Oct 7, 2026 3:05am UTC

[waleedlatif1]

@cubic-dev-ai review this PR

[cubic-dev-ai]

@cubic-dev-ai review this PR

@waleedlatif1 I have started the AI code review. It will take a few minutes to complete.

[cubic-dev-ai]

No issues found across 2 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Turn on auto-fix | Re-trigger cubic}

[cubic-dev-ai]

No issues found across 2 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Turn on auto-fix | Re-trigger cubic}

[greptile-apps]

Confidence Score: 5/5

[Medium risk] Changes how the desktop app parses tmux terminal output.

The PR appears safe to merge.

What we checked:

• Separator collisions cannot shift fields: parseFormatLines rejects records with extra fields before callers read their values.

Summary

Replaces the control-character separator with printable |~sim~| so tmux output remains readable across versions.

• Both attachment lookup and pane listing use the same separator.
• Adds an attachment regression test whose fake escapes control characters.
• waleedlatif1 explicitly accepts dropping records whose fields contain the separator, rather than reading those records incorrectly.

No actionable issues found. Tests were not run during this review.

_{Reviews (1) · Last reviewed commit: "fix(desktop): read tmux format output wi..." · Reviewed by Greptile}