fix(cli): suggest the real command instead of a plugin that does not exist

[ankitranjan7]

webcmd adapters told you to install a plugin named "adapters". There is no such plugin, and there never will be — the command is webcmd adapter, one character away.

The problem

1. rootCommandSuggestion() was a hardcoded 9-entry map. Anything not literally in it fell through to missingPluginGuidance(), which routes the caller into a plugin hunt that cannot succeed. adapters → adapter is edit distance 1 and was missed. fetch → web fetch was missed.
2. The root command:* handler called program.outputHelp(), which writes to stdout. With --json in argv that is a well-formed JSON document on stdout beside an error on stderr — anything parsing stdout reads it as success. Hosted mode did the same.
3. Unknown subcommands inside a namespace got Commander's bare unknown command 'x': no suggestion, no list of what is valid.

What changed

1. New src/command-suggest.ts: ~15-line Levenshtein (no dependency) matched against everything registered on the program — root command names, aliases, subcommand leaves (so fetch finds web fetch), installed site adapters, external CLIs. Distance ≤ 2 for tokens of 8+ chars, ≤ 1 below that; up to 3 candidates.
2. The hardcoded map stays as high-priority intent overrides (marketplace → plugin search, adapter list → adapter status) and runs before the distance engine; missingPluginGuidance is now the last resort, not the first.
3. Every built-in namespace (adapter, plugin, session, profile, daemon, external, browser, site, auth, skills) gets one shared command:* handler that prints the suggestion plus the namespace's valid subcommands. The one-off browser.on('command:*') handler and its retired-fork map moved into the shared path. Site adapter groups keep Commander's own suggestion so hosted mode stays byte-compatible.
4. No help on stdout on any error path, in local and hosted mode (src/hosted/runner.ts dropped the root-help stdout payload from three throws).
5. Before claiming "Site X is not installed", check ~/.webcmd/plugins/<X> and ~/.webcmd/clis/<X>. If the directory is there, say the adapter failed to load and point at WEBCMD_VERBOSE=1 instead of sending the user shopping.

Before / After

# before
$ webcmd adapters --json 1>/tmp/out 2>/tmp/err ; echo $?
2
$ wc -c /tmp/out
2410 /tmp/out          <- entire root help, valid JSON, on stdout
$ cat /tmp/err
Site "adapters" is not installed.
Search: webcmd plugin search adapters
Install using the installSource returned by search.

$ webcmd fetch --url https://x.com
Site "fetch" is not installed.
Search: webcmd plugin search fetch
Install using the installSource returned by search.
Usage: webcmd [options] [command]
...

$ webcmd adapter list rest
error: unknown command 'list'
ok: false
error:
  code: UNKNOWN
  message: 'error: unknown command ''list'''
  exitCode: 1

# after
$ webcmd adapters --json 1>/tmp/out 2>/tmp/err ; echo $?
2
$ wc -c /tmp/out
0 /tmp/out
$ cat /tmp/err
Unknown command "adapters".
Did you mean: webcmd adapter

$ webcmd fetch --url https://x.com
Unknown command "fetch".
Did you mean: webcmd web fetch

$ webcmd adapter list rest
error: unknown command 'list'
Did you mean: webcmd adapter status
Valid webcmd adapter commands: override, path, reset, source, status

$ webcmd zzzqqqwww
Site "zzzqqqwww" is not installed.
Search: webcmd plugin search zzzqqqwww
Install using the installSource returned by search.

Tests

src/command-suggest.test.ts (11 cases): adapters → adapter; fetch → web fetch; marketplace override wins over distance; adapter list → adapter status plus the valid-subcommand list; retired browser fork names its replacement; an installed-but-unregistered directory reports a load failure, not a missing plugin; a genuinely unknown token still gets plugin-search guidance; and both error paths write zero bytes to stdout while exiting 2.

Updated existing expectations in src/cli.test.ts, src/hosted/runner.test.ts, src/hosted/root-command-surface.test.ts, and src/hosted/main-lifecycle.test.ts that asserted root help lands on stdout during an error.

npm run typecheck clean. npx vitest run --project unit: 2712 passed, 2 failed — both in src/browser/run/playwright-client-build.test.ts, both failing identically on origin/main in this worktree (the sandbox build script cannot resolve node_modules/playwright-core here). Unrelated to this change.

🤖 Generated with Claude Code

[github-actions]

🟠 Maintainer review suggested — low confidence

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This review is advisory and does not block merging.