feat(commands): add /editor command to compose messages in $EDITOR

[Linux2010]

What added

New /editor (alias /edit) slash command that opens the user's preferred text editor (EDITOR, VISUAL, or auto-detected nano/vim/vi) to compose long messages. Save and close to queue the message; leave empty to cancel.

> /editor
Opening vim... Save and close to send, leave empty to cancel.
(847 chars from editor) Queued for the next turn.

Target Users

Gateway platform users (Telegram, Discord, Slack, WhatsApp, Signal):

• No keyboard shortcuts available in messaging platforms
• /editor is the only way to use external editor on these platforms

CLI users: See #7941 for a better solution (Ctrl+G shortcut + paste collapse)

Related Work

• feat(cli): add editor workflow for drafts #7941 by @lumenradley: Ctrl+G shortcut for CLI + large paste collapse
• [UX] Add /editor command to compose messages in $EDITOR #7262 (Issue for feat(cli): add editor workflow for drafts #7941): External editor for CLI drafts
• feat: add /editor command to compose messages in $EDITOR #7263 (Issue for this PR): External editor for Gateway platforms

Both PRs are complementary, not competing:

• feat(cli): add editor workflow for drafts #7941 → CLI users (prompt_toolkit native open_in_editor())
• feat(commands): add /editor command to compose messages in $EDITOR #7620 → Gateway users (slash command is the only option)

Implementation

File	Change
hermes_cli/commands.py	Added CommandDef for "editor" with "edit" alias
gateway/run.py	Added _handle_editor_command() method (88 lines)

Editor detection: $EDITOR → $VISUAL → auto-detect (nano → vim → vi)

Message handling: Uses same pattern as /queue — queues in adapter._pending_messages

Comment stripping: Lines starting with # are ignored (hint comments)

Why this is minimal

• Only 91 lines in gateway/run.py + 2 lines in commands.py
• Uses existing pattern (same as /queue)
• Uses existing imports (subprocess, tempfile, shlex)
• No changes to core agent loop

What I tested

Added test suite tests/gateway/test_editor_command.py with 8 test cases.

Python syntax validated for all files.

What I intentionally did not change

• No changes to CLI (prompt_toolkit) — feat(cli): add editor workflow for drafts #7941 handles that better
• No changes to agent conversation loop
• No opportunistic refactoring

Fixes #7263

Note: For CLI users, recommend using #7941 (Ctrl+G) instead — it's more ergonomic and includes paste collapse.

[lumenradley]

FYI, done with Shortcut instead of command, to be able to go into edit latter not only from empty message #7941

[alt-glitch]

Likely duplicate of #7977 and #9401 — same /editor compose command. Also related to #4774 (Ctrl+G external editor). Original issue: #7262/#7263.