Feature: Semantic History — resolve bare filenames against OSC 7 CWD on Cmd+click

[jiseongnoh]

Feature Request

When a bare filename (e.g. README.md, src/main.py) appears in terminal output, Cmd+clicking it should resolve it against the current working directory (known via OSC 7) and open it if the file exists.

This is the single biggest workflow gap between cmux and iTerm2 for AI coding agent users.

Current behavior

• https://google.com → clickable ✅ (URL pattern auto-detected)
• /Users/krust/project/file.md → clickable ✅ (absolute path detected)
• file.md → not clickable ❌ (not recognized as a file)
• src/components/App.tsx → not clickable ❌

Expected behavior

1. User Cmd+clicks file.md in terminal output
2. cmux already knows CWD via OSC 7 (e.g. /Users/krust/project)
3. cmux checks: does /Users/krust/project/file.md exist?
4. Yes → open in default editor (or cmux markdown panel for .md)
5. No → fall through to current behavior

Why this matters

AI coding agents (Claude Code, Codex, etc.) constantly output bare filenames:

I've updated the following files:
  proposal_draft.md
  workflow_v2.md
  src/coordinator.ts

In iTerm2, every one of these is Cmd+clickable via Semantic History. In cmux, none of them are. This is the #1 reason some users stay on iTerm2 instead of switching to cmux full-time.

Technical context

• cmux already receives OSC 7 from the shell (zsh chpwd hook) — the CWD is known
• Ghostty's resolvePathForOpening() in Surface.zig:2083 already does CWD-relative resolution for regex-detected links, so precedent exists upstream
• Related: Terminal link clicks apply browser omnibar heuristics to relative file paths #1154 (relative paths in OSC 8 hyperlinks misrouted to browser URL)
• Related upstream: anthropics/claude-code#13008 (Claude Code emitting OSC 8 for file paths)

Suggested approach

On Cmd+click of any non-URL text:

1. Get CWD from last OSC 7 report
2. stat(CWD + "/" + clicked_text) — does the file exist?
3. If yes and has line number suffix (e.g. file.md:42), open at that line
4. If yes, open via system handler (or cmux internal panel for supported types)
5. If no, fall through to existing behavior

Environment

• cmux nightly
• macOS 15.5 (Darwin 24.6.0)
• Primary use case: Claude Code AI coding agent

[teamleaderleo]

@jiseongnoh Thank you for the idea and for opening the PR yourself!! #2200 is open to resolve bare filenames like README.md against the shell's working directory on Cmd+click. Related work on opening path:line links in your editor is also in progress in #7162 :)