feat(rig): the doctor can name what a fresh box is missing, before the audio arrives

rig-doctor's samples check had a structural hole I only saw once it ran: it
shells out to sample-pack, which resolves bank names by walking the Dirt-Samples
tree of the box it is running on. On PLN's laptop that is 281 banks and looks
fine. On an empty XPS24 it reports "0 banks resolve" — true, and useless. The
check could never say "281 missing", which is the only thing a fresh machine
needs to hear.

The fix is an EXTERNAL reference, committed: sample-manifest.json at the repo
root (463 KB, 281 banks, 9385 filenames, generated by tools/sample-pack.py
--all). rig-doctor now falls back to it when no --bundle is given, and --bundle
accepts a manifest FILE as well as a bundle directory. So the ordering that
makes a same-day setup possible works: git clone, run the doctor, get the exact
list of missing banks — all before 15 GB of audio has moved anywhere.

Committed deliberately, not gitignored. A generated artifact that nothing ever
compares against reality is how preload.scd drifted for weeks and made its
debut as a crackle at a venue. This one is diffable, and its own freshness is
visible in git.

Mutation-verified rather than assumed, because a checker that cannot report
absence is exactly the failure being fixed here: planted two nonexistent banks
in a copy of the manifest, confirmed the check goes FAIL, names them, counts
2/281 with sizes, and flips the final verdict from "yes" to "no".

That test also exposed a fix-pointer that could not be followed — with a
manifest file it said "see <manifest.json>/README.md", a path that cannot
exist. Now _bundle_fix() distinguishes the three cases: you have the bundle
directory (cp from it), you have a bundle's MANIFEST.json (cp from its parent),
or you have only the committed list (rsync from the freebox staging copy, or
rebuild with sample-pack on a box that has the samples). A fix you cannot follow
is not a fix.

The carry-on bundle it describes is built and verified: 281 banks, 9385 files,
15,108,195,468 bytes, checked file-by-file against its own manifest with 0
mismatches, and staged to /mnt/freebox/PLN/parvagues-carryon byte-identical
(9387 files both sides, 21m53s over SMB at ~11 MB/s).

903 passed, 0 failed.

tools/rig-doctor.py

@@ -481,6 +481,29 @@ def check_scd_sample_roots() -> None:
                 f"create {checkdir}, or fix the path in start_and_midi.scd")
 
 
+def _bundle_fix(bundle: Path, dirt: Path) -> str:
+    """Where to actually GET the missing banks.
+
+    The manifest and the audio are deliberately separate: the manifest is
+    committed so a fresh box knows what it lacks the moment it has the clone,
+    while 15 GB of audio arrives by other means. So the fix text has to
+    distinguish "you have the bundle, copy from it" from "you only have the
+    list, go fetch the bundle" — pointing a reader at MANIFEST.json/README.md
+    is a dead end, and a fix that cannot be followed is not a fix.
+    """
+    tail = ("every folder travels WHOLE — never subset one, because bank:N "
+            "indexes files in glob order and dropping one renumbers the rest")
+    if bundle.is_dir():
+        return f"cp -r {bundle}/<bank> {dirt}/   ({tail})"
+    if bundle.name == "MANIFEST.json":
+        return f"cp -r {bundle.parent}/<bank> {dirt}/   ({tail})"
+    # The committed repo manifest: the list, not the audio.
+    return ("this is the committed bank LIST, not the audio. Get the bundle: "
+            f"rsync -a /mnt/freebox/PLN/parvagues-carryon/ {dirt}/  "
+            "— or rebuild it on a box that has the samples with "
+            f"tools/sample-pack.py --all --pack DEST   ({tail})")
+
+
 def check_sample_coverage(bundle: Path | None) -> None:
     """Does this box have the banks the set needs?
 
@@ -523,6 +546,18 @@ def check_sample_coverage(bundle: Path | None) -> None:
         return
 
     if bundle is None:
+        # Fall back to the manifest COMMITTED at the repo root. This is the
+        # ordering that makes a same-day setup possible: a fresh box can be
+        # told exactly which banks it lacks the moment it has the git clone,
+        # BEFORE the 15 GB of audio arrives. Without it this check is
+        # structurally self-referential -- sample-pack resolves names against
+        # the box it runs on, so an empty machine reports "0 banks resolve"
+        # rather than "281 missing", which is true and useless.
+        default = REPO_ROOT / "sample-manifest.json"
+        if default.is_file():
+            bundle = default
+
+    if bundle is None:
         mapped = report["banks"]["mapped"]
         extra = report["banks"]["extra"]
         n = len(mapped) + len(extra)
@@ -536,7 +571,11 @@ def check_sample_coverage(bundle: Path | None) -> None:
             f"overridden downstream ('#' is '|>').")
         return
 
-    manifest_path = bundle / "MANIFEST.json"
+    # Accept either a bundle DIRECTORY or a manifest FILE. The committed
+    # sample-manifest.json at the repo root is the whole point: a fresh box can
+    # be told exactly which 281 banks it is missing BEFORE the 15 GB arrives,
+    # which is the one ordering that makes a same-day setup possible.
+    manifest_path = bundle if bundle.is_file() else bundle / "MANIFEST.json"
     if not manifest_path.is_file():
         add("SAMPLES", "sample coverage", WARN,
             f"--bundle {bundle} given but no MANIFEST.json there")
@@ -575,9 +614,7 @@ def check_sample_coverage(bundle: Path | None) -> None:
             f"{len(missing_names)}/{total} banks missing "
             f"(~{human(missing_bytes)}, {missing_files} files): "
             f"{sample_names}{more}{unresolved_note}",
-            f"drop the missing folders from {bundle} into "
-            f"{dirt}/  (see {bundle}/README.md — every folder travels whole, "
-            f"never subset one: bank:N indexing depends on file order)")
+            _bundle_fix(bundle, dirt))
 
 
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