[raiseCatError]

Draft, do not merge before v0.21 ships. #430 has carried dev into release/v0.21.0; a fix v0.21's physical QA needs would reach the release the same way, so anything merged into dev before the release would ride along. Part of v0.22 (#431).

Why

#366 asks for clearer paths between NMSh's native surfaces and the editors people already use, reusing installed tools rather than building editors. /view could hand a file only to the native /edit (e), and its own notes for a partly shown or undecodable file said "less or an editor" without a way to get there. /open already knows how to reach the person's editor safely.

What changed

• o in /view of a file sends the file and the first line on screen to the same bridge /open uses (resolveHostActions, Settings → Open with):
  • Zed / VS Code (around NMSh, or chosen in Open with): launched with argv, the viewer stays, its status says Opened in Zed. (or why it could not start).
  • A terminal editor from $VISUAL/$EDITOR: its command (nvim +41 /path/notes.txt, hx '/path/my notes.txt:41'), quoted for the session's shell, goes in the composer for the person to run — never run for them — and the viewer closes so it is in view.
  • A draft already in the composer is never replaced: the viewer says so instead.
  • No editor known: the viewer shows the bridge's reason (set VISUAL/EDITOR, or choose Open with).
• Rendered Markdown rows are not source lines, so the file then opens at its start; the source view (m) keeps the line. Stored output is not a file and offers nothing new.
• The truncation notes and the UTF-16 refusal now name this way to the rest; Ask's /view description lists e and o. Footer: e edit · o open in editor.

No new launcher, editor registry or PTY ownership; paths stay single argv elements; nothing runs without the person's Enter.

Verification

• New tests fail before the change (5 of 5) and pass after: tests/viewerOpenEditor.test.ts drives the real key handler and the real bridge with a fake host (terminal editor at the line shown with nothing executed — the capture session throws on any submission; a file named my notes; rm -rf ~ $(x).txt kept as one quoted argument; a draft left alone; a GUI editor launched, a launch failure and no editor reported, viewer kept open) and tests/viewer.test.ts (key → action for files, Markdown rendered vs. source, output; footer; notes).
• Focused: viewer, viewer app, host actions and Ask suites — 125/125. npm run verify:fast — pass.
• Full canonical npm run verify on 5d81d93e (NMSH_TEST_TMPDIR=/Volumes/T7Tmp/ai-dev, load 4–13): exit 0, 3,148 tests, 3,146 pass, 2 skipped, 0 failed.

Physical QA (not done)

Checklist: docs/testing/v022-physical-qa.md pass 2 (in #435). Ghostty and Terminal.app: /view a long file, scroll, o with EDITOR=nvim (composer gets nvim +N file; Enter opens it at that line; quitting returns to NMSh), with EDITOR unset outside an editor (the viewer explains), and inside Zed's and VS Code's integrated terminals (the file opens there at the line). Narrow width: the footer wraps and Esc stays reachable.

Refs #366