fix(t3x): auto-build defects found running the LaunchAgent for real

[radroid]

Setting the auto-build up end-to-end on a real machine surfaced three defects. All three
were invisible to the test suite because they only manifest under launchd, or only when
no build exists yet.

1. --print-launchd emitted a plist that can never run

macOS TCC gates ~/Documents, ~/Desktop, ~/Downloads and iCloud Drive. LaunchAgents
get no TCC grant and — unlike apps — never trigger a consent prompt; macOS just returns
EPERM.

Verified with a probe agent that differed only by path:

Path	launchd	Terminal
~/Documents/t3code/…	EPERM	OK
identical file copied to /tmp	OK	OK
listing ~/Documents/t3code	EPERM	OK

The failure mode is the bad kind: launchctl bootstrap succeeds, launchctl print reports
the job as loaded, and the only evidence is last exit code = 126. It looks installed and
silently never builds.

Now refuses to emit (exit 2) with the three remedies, or --force past it.

2. --install --dry-run named the wrong app

It hardcoded "${T3X_AUTOBUILD_APP_NAME:-T3 Code}.app" and never looked at the dmg — so it
always reported T3 Code.app while a real install replaced T3 Code (Alpha).app. Wrong
about the single fact the preview exists to establish. It also returned before printing
anything when no dmg had been built, i.e. for every first-time user.

Now mounts the dmg read-only for ground truth, falls back to a mirror of upstream's
resolveDesktopProductName(), and warns when the target app is absent — the footgun
where --install silently creates a third app and leaves the one you actually run alone.

3. log() wrote every line twice under launchd

tee -a "$LOG_FILE" >&2 echoes to stderr, and the plist points both StandardOutPath
and StandardErrorPath at that same file. One watcher's output reads exactly like two
racing — which is how this was noticed.

The plist now declares T3X_AUTOBUILD_STDERR_IS_LOG=1. Detecting it via
stat -f '%d:%i' /dev/fd/2 is deliberately not used and is documented in-line: on
macOS that stats the devfs node (2540177495:339), never the redirect target, so it can
never match. I tried it first; it silently didn't work.

Verification

• TCC guard: real git repo under ~/Documents → exit 2, 0 bytes on stdout, remedies on stderr
• No false positive from ~/Developer → exit 0, valid 1302-byte plist (plutil -lint OK)
• --force still emits
• dry-run with dmg → read 'T3 Code (Alpha).app' from …; without dmg → predicted from apps/desktop/package.json; env override still wins
• absent-target warning fires; /Applications verified untouched by all dry runs
• launchd-style dual redirect: 1 occurrence per line (was 2); terminal mode unchanged (3 stderr lines, 3 file lines)
• bash -n clean

🤖 Generated with Claude Code

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