Deliver a remote loop's shed prompt on a channel that can fail

[scgopi]

The bug

A loop on a Codespace booted with its entire brief being a pointer, and the file was not there:

Your complete instructions are in the file at ~/.graphcode/memory/codespace---…/PROMPT.md — read that file first
Read PROMPT.md — Path does not exist

Cause

When a goal overruns the ~1 KB line zmx types into a session, the launch sheds it to PROMPT.md and types a short pointer (#57). For a remote project the file rode remoteDeliveryScript's manifest — one python3 -c carrying the 45 KB CLI shim, the briefing and the wake digest, ~105 KB of base64 in a single argv string (Linux caps one at 128 KiB), ending in || true.

That neutering is correct for everything else in the manifest: a session without its briefing is still a session, and delivery must never block a launch. It is wrong for the prompt, which is the instructions. And #345 made it common — shedding now moves the prompt to a file before it drops the briefing, so far more remote loops launch pointered. Any failure in that one best-effort command produced a live, running agent with nothing to do.

Fix

The prompt gets its own delivery: a small installer carrying one file, un-neutered, &&-chained into the fresh launch inside the create branch.

• A failed delivery takes the launch with it — the node stays honestly not-running and the next liveness sweep retries, the posture startRemote already takes on a failed dial.
• It logs prompt-undelivered to the remote dial log, so the failure is diagnosable instead of surfacing only as an agent saying its instructions do not exist.
• It no longer shares the shim's payload size, and runs only when a launch is actually about to happen.
• The resume branch is untouched: a resumed conversation needs no prompt.
• Loops whose prompt fits the typed line pay nothing — no second installer, no extra gate.

Not addressed here: the wake digest still rides the best-effort manifest. A missing memory degrades (the loop wakes without what past passes learned); a missing prompt does not.

Verification

Worktree gate, private DerivedData, literal exit codes:

Step	Result
xcodebuild -scheme graphcode build	exit=0
xcodebuild -scheme graphcode test	exit=0, ** TEST SUCCEEDED **, Test run with 1900 tests in 199 suites passed
xcodebuild -scheme graphcode-cli build	exit=0
xcodebuild -scheme graphcoded build	exit=0
swiftlint lint	0 errors
swift format lint --recursive --strict	exit=0

TDD evidence

RED: xcodebuild test -only-testing:graphcodeTests/RemoteSessionLaunchTests with main's ZmxSessionLauncher.swift and RemoteGraphAccess.swift in place -> exit=65, theBestEffortManifestNeverCarriesThePrompt failed on "files.keys.contains PROMPT.md"

GREEN: xcodebuild -scheme graphcode -destination platform=macOS test -> exit=0, ** TEST SUCCEEDED **, Test run with 1900 tests in 199 suites passed

REGRESSION: full suite plus graphcode-cli and graphcoded builds, swiftlint and swift format lint -> exit=0 on every step, 0 lint errors, the 1897 pre-existing tests all still pass

The other three new tests need API this branch adds, so they cannot run against main at all.