Freeze the package compatibility corpus: real .rsbank bytes proving both ladder directions, every truncation site, and the round trip

tests/fixtures/package_compat/README.md

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+# The frozen `.rsbank` compatibility corpus
+
+Real RSBK bytes, committed. `tests/test_package_compat.cpp` decodes them;
+`tests/test_package_round_trip.cpp` drives them through the import and export verbs.
+
+## THE RULE: this corpus is append-only
+
+**No file here is ever regenerated or edited.** When a future format version ships, add
+its fixture beside these and leave every existing one alone.
+
+The reason is the whole point of the corpus. These bytes exist to catch a format change
+that quietly breaks a compatibility direction. A fixture regenerated by the build that
+broke it agrees with that build by construction and catches nothing — which is exactly
+the failure mode a version ladder exists to prevent. The same argument forbids a test
+that builds its own fixture at run time.
+
+If a fixture stops decoding, the answer is never to re-cut the fixture. Either the format
+change was structural (bump `minReaderVersion`, add a new fixture, and leave the old one
+asserting the refusal) or it is a regression.
+
+## Provenance
+
+`v1_shipping.rsbank` was produced by running this repo's own export verb (`exportBank`)
+at version **1.4.0** over a one-sample bank, and copying the emitted file here verbatim.
+Every other fixture is derived from those bytes: the truncations are prefixes of them,
+and the synthetic packages reuse their manifest region under different version integers
+or a hand-written hostile manifest (the encoder refuses to write one, which is why those
+could not come from the verb).
+
+Payloads are one 300-byte 16-bit mono WAV. The properties under test are structural —
+version integers, framing arithmetic, name validation — so a larger payload proves
+nothing extra and costs the repo bytes forever. Whole corpus: ~14 KB.
+
+Adding a fixture for a future version means writing it with **that** version's shipping
+build, exactly as this one was, and recording the build's version here.
+
+## What each fixture proves
+
+### The three version fixtures
+
+| File | `formatVersion` / `minReaderVersion` | Verdict | Proves |
+|---|---|---|---|
+| `v1_shipping.rsbank` | 1 / 1 | `Readable` | This build reads what it wrote: header, one manifest entry, the entry digest, and every `Sample` field with every optional present. Writer semver `1.4.0` is asserted **literally**, not against `stampVersion()` — comparing against the running build would let a version bump re-anchor the fixture silently. |
+| `additive_forward.rsbank` | 2 / 1 | `Readable` | An additive newer writer still reads. Carries three keys this build has never heard of — `exportTool` at the manifest root, `futureEntryKey` on the entry, `futureSampleKey` inside the nested `Sample` blob — and decodes to *exactly* the manifest `v1_shipping.rsbank` decodes to. Writer semver `1.9.0`. |
+| `refuse_structural.rsbank` | 2 / 2 | `TooNew` | A structural newer writer is refused whole. The header through the writer semver still reads, so the refusal can name all three facts (`1.9.0`, needs format 2, this build reads 1); no manifest, no layout, no partial success. Its body is `v1_shipping.rsbank`'s own manifest, which parses — so the refusal is a **decision**, not an inability. |
+
+### Truncation — one file per distinct decode failure site
+
+Each is a prefix of `v1_shipping.rsbank` (907-byte prefix + 300-byte payload = 1207
+bytes). All classify `Malformed`; none may classify `TooNew`, since "install a newer
+build" does not fix a partial download.
+
+| File | Bytes | Site the cut lands in |
+|---|---|---|
+| `trunc_magic.rsbank` | 2 | Inside the 4-byte magic. |
+| `trunc_version_pair.rsbank` | 10 | Inside the frozen header's `minReaderVersion` u32. |
+| `trunc_writer_semver.rsbank` | 18 | Inside the frozen header's writer semver. |
+| `trunc_manifest_length.rsbank` | 23 | Inside the manifest-length u32. |
+| `trunc_manifest_body.rsbank` | 466 | Inside the manifest JSON. |
+| `trunc_payload_start.rsbank` | 907 | At the payload boundary. RSBK stores no layout section — the layout is derived from the manifest's entries — so this is the cut that exercises "manifest parses, layout computes, exact-size proof fails". |
+| `trunc_payload_middle.rsbank` | 1057 | Inside the first payload. |
+| `trunc_one_short.rsbank` | 1206 | One byte short of the total. |
+
+### Hostile names — refused at decode, before any planner
+
+The two naming fields carry different rules (`src/core/package/CLAUDE.md`), so each
+fixture keeps the other field spelled cleanly (`kick.wav`) and the refusal is
+attributable to the field under test.
+
+Entry name — a bare file name, no path expression possible (`isValidEntryName`):
+
+| File | Entry name |
+|---|---|
+| `hostile_name_dotdot.rsbank` | `..` |
+| `hostile_name_parent_slash.rsbank` | `../evil.wav` |
+| `hostile_name_parent_backslash.rsbank` | `..\evil.wav` |
+| `hostile_name_subdir_slash.rsbank` | `sub/evil.wav` |
+| `hostile_name_drive_absolute.rsbank` | `C:\Windows\evil.wav` |
+| `hostile_name_unc_absolute.rsbank` | `\\srv\share\evil.wav` |
+
+Nested `Sample::relativePath` — a path by design, refused only for traversal and
+absolute forms (`isValidNestedSamplePath`):
+
+| File | `relativePath` | Guard that fires first inside the codec |
+|---|---|---|
+| `hostile_path_dotdot_slash.rsbank` | `bank/../../evil.wav` | `isValidNestedSamplePath` |
+| `hostile_path_dotdot_backslash.rsbank` | `bank\..\evil.wav` | `isValidNestedSamplePath` |
+| `hostile_path_rooted.rsbank` | `/etc/evil.wav` | `BankModel::add`'s absolute-path rejection, which drops the record and leaves the nested blob holding zero samples |
+| `hostile_path_drive_absolute.rsbank` | `C:\Windows\evil.wav` | as above |
+| `hostile_path_unc_absolute.rsbank` | `\\srv\share\evil.wav` | as above |
+
+Both guards are inside the codec and both refuse the whole package, so the security
+property is the same either way; the split is recorded because a change to either guard
+alone would still leave these fixtures passing.
+
+### The round-trip anchor
+
+`v1_shipping.rsbank` doubles as it: the file **is** a real export, so importing it and
+exporting the resulting bank closes export → import → export over frozen bytes. Entry
+names may legally change across the trip (the importer re-spells a bank file, the
+exporter mints its own transport name); the payload bytes may not.

tests/fixtures/package_compat/trunc_magic.rsbank

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+RS

tests/package_fixtures.h

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+#pragma once
+// The one accessor over the frozen package-compat corpus (tests/fixtures/package_compat).
+// REASAMPLER_PACKAGE_FIXTURE_DIR is a compile-time absolute path defined by each
+// consuming test target: the corpus is source-tree data, and a test's working directory
+// under ctest differs between single- and multi-config generators, so no relative
+// spelling reaches it from both.
+//
+// Every caller must check the returned size: a fixture that failed to open reads as an
+// empty buffer, which a "this must be Malformed" assertion would otherwise pass.
+
+#include <cstdint>
+#include <fstream>
+#include <iterator>
+#include <string>
+#include <vector>
+
+inline std::string packageFixturePath(const std::string& name) {
+    return std::string(REASAMPLER_PACKAGE_FIXTURE_DIR) + "/" + name;
+}
+
+inline std::vector<std::uint8_t> packageFixtureBytes(const std::string& name) {
+    std::ifstream f(packageFixturePath(name), std::ios::binary);
+    return std::vector<std::uint8_t>(std::istreambuf_iterator<char>(f),
+                                     std::istreambuf_iterator<char>());
+}

tests/test_package_compat.cpp

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+// Standalone tests over the FROZEN package-compat corpus — no REAPER, no framework.
+// Nothing here builds a package: every byte comes off disk exactly as committed, which
+// is the only shape in which a later format change can be caught breaking a
+// compatibility direction. A test that re-derived its own fixture would prove only that
+// the codec agrees with itself. See tests/fixtures/package_compat/README.md.
+//
+// The values pinned below are the FIXTURE's facts, not this build's — the writer semver
+// especially must never be compared against version::stampVersion(), or a version bump
+// would silently re-anchor the corpus.
+
+#include "../src/core/package/bank_package.h"
+
+#include <cstdint>
+#include <cstdio>
+#include <string>
+#include <vector>
+
+#include "../src/core/package/package_format.h"
+#include "../src/core/package/package_manifest.h"
+#include "package_fixtures.h"
+
+using namespace reasampler::package;
+using namespace reasampler::model;
+
+static int g_fail = 0;
+#define CHECK(cond) do { if(!(cond)) { \
+    std::printf("FAIL line %d: %s\n", __LINE__, #cond); ++g_fail; } } while(0)
+
+// --- what the v1 fixture's bytes say -----------------------------------------
+
+static constexpr const char* kV1File = "v1_shipping.rsbank";
+static constexpr const char* kV1WriterSemver = "1.4.0";
+static constexpr const char* kV1EntryName = "kick.wav";
+static constexpr const char* kV1EntryHash = "8df36e805531e4af";
+static constexpr std::uint64_t kV1PrefixSize = 907;
+static constexpr std::uint64_t kV1PayloadLength = 300;
+static constexpr std::uint64_t kV1TotalSize = 1207;
+
+// Every Sample field the shipping build wrote, with every optional PRESENT — so
+// "every known field intact" is a claim about the whole record, not a sampled few.
+// relativePath is the BARE transport name: export_plan normalizes it (see
+// src/core/package/CLAUDE.md), so a package carrying a directory component here would
+// mean the fixture predates that rule.
+static Sample expectedV1Sample() {
+    Sample s;
+    s.id = "cap-kick";
+    s.displayName = "Kick (wet)";
+    s.relativePath = "kick.wav";
+    s.sourceMode = SourceMode::RazorArea;
+    s.sourceRange = {1.25, 3.5, 480.0, 1920.0};
+    s.trackGuids = {"{AAA}", "{BBB}"};
+    s.wetDry = 0.75;
+    s.channelCount = 1;
+    s.sampleRate = 48000;
+    s.lengthSeconds = 0.0026666666666666666;
+    s.lengthBeats = 0.00533;
+    s.captureTempo = 120.5;
+    s.captureTimeSigNum = 7;
+    s.captureTimeSigDenom = 8;
+    s.key = "F#m";
+    s.rootNote = 60;
+    s.loop = LoopPoints{8, 120};
+    s.levels = {-0.3, -12.7, -14.0};
+    s.clipped = true;
+    s.tier = Tier::Archive;
+    s.contentHash = "Wcompatcorpus0001";
+    s.provenance = Provenance{"cap-parent", "fx-snapshot"};
+    s.createdTimestamp = 1754000000;
+    return s;
+}
+
+static PackageManifest expectedV1Manifest() {
+    PackageManifest m;
+    m.bankDisplayName = "Compat Corpus";
+    m.exportTimestamp = 1754100000;
+    m.entries.push_back({kV1EntryName, kV1PayloadLength, kV1EntryHash, expectedV1Sample()});
+    m.slots.append("cap-kick");
+    return m;
+}
+
+// A fixture that failed to open reads as an empty buffer, and an empty buffer decodes
+// Malformed — which would let half this file pass vacuously. Every suite loads through
+// here.
+static std::vector<std::uint8_t> load(const char* name, std::size_t expectedSize) {
+    std::vector<std::uint8_t> bytes = packageFixtureBytes(name);
+    if (bytes.size() != expectedSize) {
+        std::printf("FAIL: fixture %s is %zu bytes, expected %zu (path: %s)\n", name,
+                    bytes.size(), expectedSize, packageFixturePath(name).c_str());
+        ++g_fail;
+    }
+    return bytes;
+}
+
+static bool containsToken(const std::vector<std::uint8_t>& bytes, const std::string& token) {
+    const std::string text(reinterpret_cast<const char*>(bytes.data()), bytes.size());
+    return text.find(token) != std::string::npos;
+}
+
+static std::uint32_t le32At(const std::vector<std::uint8_t>& bytes, std::size_t at) {
+    return static_cast<std::uint32_t>(bytes[at]) |
+           (static_cast<std::uint32_t>(bytes[at + 1]) << 8) |
+           (static_cast<std::uint32_t>(bytes[at + 2]) << 16) |
+           (static_cast<std::uint32_t>(bytes[at + 3]) << 24);
+}
+
+// --- direction 1: the shipping build reads what it wrote ---------------------
+
+// The header pair as the bytes carry it, classified without going through decode — the
+// ladder rule stated against the file rather than against the decoder's reading of it.
+static PackageReadability classifyFixture(const std::vector<std::uint8_t>& bytes) {
+    return classifyPackageVersion(le32At(bytes, 4), le32At(bytes, 8));
+}
+
+static void testV1FixtureDecodesToTheRecordTheShippingBuildWrote() {
+    const std::vector<std::uint8_t> bytes = load(kV1File, kV1TotalSize);
+    CHECK(classifyFixture(bytes) == PackageReadability::Readable);
+
+    const DecodedPackage dec = decodePackage(bytes, bytes.size());
+    CHECK(dec.status == PackageReadability::Readable);
+    CHECK(dec.header.formatVersion == 1);
+    CHECK(dec.header.minReaderVersion == 1);
+    CHECK(dec.header.writerVersion == kV1WriterSemver);
+
+    CHECK(dec.manifest.entries.size() == 1);
+    CHECK(dec.manifest.bankDisplayName == "Compat Corpus");
+    if (dec.manifest.entries.size() == 1) {
+        CHECK(dec.manifest.entries[0].fileName == kV1EntryName);
+        CHECK(dec.manifest.entries[0].byteLength == kV1PayloadLength);
+        CHECK(dec.manifest.entries[0].byteHash == kV1EntryHash);
+        CHECK(dec.manifest.entries[0].sample == expectedV1Sample());
+    }
+    CHECK(dec.manifest == expectedV1Manifest());
+
+    CHECK(dec.prefixSize == kV1PrefixSize);
+    CHECK(dec.layout.size() == 1);
+    if (dec.layout.size() == 1) {
+        CHECK(dec.layout[0].name == kV1EntryName);
+        CHECK(dec.layout[0].offset == kV1PrefixSize);
+        CHECK(dec.layout[0].length == kV1PayloadLength);
+    }
+}
+
+// --- direction 1: a NEWER additive writer still reads ------------------------
+
+// formatVersion N+1, minReaderVersion unchanged: the whole reason two integers exist.
+// The fixture carries three keys this build has never heard of — one at the manifest
+// root, one on the entry, one inside the nested Sample blob — and must still decode to
+// exactly what the v1 fixture decodes to.
+static void testAdditiveForwardFixtureReadsWithEveryKnownFieldIntact() {
+    const std::vector<std::uint8_t> bytes = load("additive_forward.rsbank", 1283);
+
+    // Non-vacuity: the unknown keys are genuinely in the bytes, so the equality below
+    // is "skipped without error", not "there was nothing to skip".
+    CHECK(containsToken(bytes, "\"exportTool\""));
+    CHECK(containsToken(bytes, "\"futureEntryKey\""));
+    CHECK(containsToken(bytes, "\"futureSampleKey\""));
+
+    CHECK(classifyFixture(bytes) == PackageReadability::Readable);
+
+    const DecodedPackage dec = decodePackage(bytes, bytes.size());
+    CHECK(dec.status == PackageReadability::Readable);
+    CHECK(dec.header.formatVersion == kPackageFormatVersion + 1);
+    CHECK(dec.header.minReaderVersion == kPackageMinReaderVersion);
+    CHECK(dec.header.writerVersion == "1.9.0");
+
+    // Every known field, end to end: same manifest the v1 fixture yields.
+    CHECK(dec.manifest == expectedV1Manifest());
+    CHECK(dec.layout.size() == 1);
+    if (dec.layout.size() == 1) CHECK(dec.layout[0].length == kV1PayloadLength);
+}
+
+// --- direction 2: a structural newer writer is refused whole -----------------
+
+static void testRefuseFixtureIsTooNewAndStillNamesTheWriter() {
+    const std::vector<std::uint8_t> bytes = load("refuse_structural.rsbank", kV1TotalSize);
+    CHECK(classifyFixture(bytes) == PackageReadability::TooNew);
+
+    const DecodedPackage dec = decodePackage(bytes, bytes.size());
+    CHECK(dec.status == PackageReadability::TooNew);
+    // The three facts the refusal message owes the user.
+    CHECK(dec.header.formatVersion == kPackageFormatVersion + 1);
+    CHECK(dec.header.minReaderVersion == kPackageFormatVersion + 1);
+    CHECK(dec.header.writerVersion == "1.9.0");
+
+    // Nothing else: no manifest, no layout, no partial success.
+    CHECK(dec.manifest == PackageManifest{});
+    CHECK(dec.layout.empty());
+    CHECK(dec.prefixSize == 0);
+
+    // The refusal is a DECISION, not an inability: this fixture's body is the v1
+    // fixture's own manifest, which parses. Walk the frozen header by hand to lift it
+    // out — a reader at this version is forbidden from doing so, which is the point.
+    const std::size_t manifestLenAt = 16 + le32At(bytes, 12);
+    const std::uint32_t manifestLen = le32At(bytes, manifestLenAt);
+    const std::string body(reinterpret_cast<const char*>(bytes.data() + manifestLenAt + 4),
+                           manifestLen);
+    CHECK(deserializeManifest(body).has_value());
+}
+
+// --- truncation: Malformed at every site, never TooNew -----------------------
+
+// One fixture per DISTINCT decode failure site rather than an arithmetic spread. The
+// RSBK layout is derived from the manifest's entries, not stored as its own section, so
+// the site a "mid-layout" cut maps to is the payload boundary: the manifest parses, the
+// layout computes, and the exact-size proof is what fails.
+struct Truncation {
+    const char* file;
+    std::size_t size;  // the cut offset — the committed file IS this many bytes
+    const char* site;
+};
+
+static const Truncation kTruncations[] = {
+    {"trunc_magic.rsbank", 2, "inside the 4-byte magic"},
+    {"trunc_version_pair.rsbank", 10, "inside the frozen header's minReaderVersion u32"},
+    {"trunc_writer_semver.rsbank", 18, "inside the frozen header's writer semver"},
+    {"trunc_manifest_length.rsbank", 23, "inside the manifest-length u32"},
+    {"trunc_manifest_body.rsbank", 466, "inside the manifest JSON"},
+    {"trunc_payload_start.rsbank", 907,
+     "at the payload boundary — manifest parses, layout computes, exact-size proof fails"},
+    {"trunc_payload_middle.rsbank", 1057, "inside the first payload"},
+    {"trunc_one_short.rsbank", 1206, "one byte short of the total"},
+};
+
+static void testEveryTruncationIsMalformedNeverTooNew() {
+    for (const Truncation& t : kTruncations) {
+        const std::vector<std::uint8_t> bytes = load(t.file, t.size);
+        const DecodedPackage dec = decodePackage(bytes, bytes.size());
+        if (dec.status != PackageReadability::Malformed) {
+            std::printf("FAIL: %s (%s) classified %s, expected Malformed\n", t.file, t.site,
+                        dec.status == PackageReadability::TooNew ? "TooNew" : "Readable");
+            ++g_fail;
+        }
+        // A refusal never half-succeeds, at any site.
+        CHECK(dec.manifest.entries.empty());
+        CHECK(dec.layout.empty());
+        CHECK(dec.prefixSize == 0);
+
+        // The shell hands decode a PREFIX plus the observed file size, not the whole
+        // file — so the verdict has to survive that call shape too, at every cut the
+        // incremental seam can actually satisfy.
+        const auto need = requiredPrefixSize(bytes);
+        if (need && *need <= bytes.size()) {
+            const std::vector<std::uint8_t> head(bytes.begin(),
+                                                 bytes.begin() + static_cast<std::ptrdiff_t>(*need));
+            CHECK(decodePackage(head, bytes.size()).status == PackageReadability::Malformed);
+        }
+    }
+}
+
+// --- hostile names: refused at decode, before any planner exists -------------
+
+// The two fields carry DIFFERENT rules (src/core/package/CLAUDE.md): the entry name may
+// not express a path at all, while the nested relativePath is a path and is refused only
+// for traversal and absolute forms. Each fixture keeps the other field clean, so the
+// refusal is attributable to the field under test.
+struct HostileFixture {
+    const char* file;
+    std::size_t size;
+    const char* offending;   // the form as it reads once JSON-unescaped
+    bool inEntryName;        // false: the nested Sample's relativePath
+};
+
+static const HostileFixture kHostiles[] = {
+    {"hostile_name_dotdot.rsbank", 624, "..", true},
+    {"hostile_name_parent_slash.rsbank", 633, "../evil.wav", true},
+    {"hostile_name_parent_backslash.rsbank", 634, "..\\evil.wav", true},
+    {"hostile_name_subdir_slash.rsbank", 634, "sub/evil.wav", true},
+    {"hostile_name_drive_absolute.rsbank", 643, "C:\\Windows\\evil.wav", true},
+    {"hostile_name_unc_absolute.rsbank", 646, "\\\\srv\\share\\evil.wav", true},
+    {"hostile_path_dotdot_slash.rsbank", 641, "bank/../../evil.wav", false},
+    {"hostile_path_dotdot_backslash.rsbank", 640, "bank\\..\\evil.wav", false},
+    {"hostile_path_rooted.rsbank", 635, "/etc/evil.wav", false},
+    {"hostile_path_drive_absolute.rsbank", 643, "C:\\Windows\\evil.wav", false},
+    {"hostile_path_unc_absolute.rsbank", 646, "\\\\srv\\share\\evil.wav", false},
+};
+
+// A backslash rides the manifest JSON doubled; the corpus table above spells the
+// unescaped form, since that is what the naming rules are asked about.
+static std::string jsonEscaped(const std::string& s) {
+    std::string out;
+    for (char c : s) {
+        if (c == '\\') out += '\\';
+        out += c;
+    }
+    return out;
+}
+
+static void testEveryHostileNameIsRefusedAtDecode() {
+    // The clean spelling both fields hold in the fixture they are NOT under test in —
+    // without this, a refusal could be coming from the wrong field.
+    CHECK(isValidEntryName("kick.wav"));
+    CHECK(isValidNestedSamplePath("kick.wav"));
+
+    for (const HostileFixture& h : kHostiles) {
+        const std::vector<std::uint8_t> bytes = load(h.file, h.size);
+        if (!containsToken(bytes, jsonEscaped(h.offending))) {
+            std::printf("FAIL: %s does not carry the form it is named for (%s)\n", h.file,
+                        h.offending);
+            ++g_fail;
+        }
+
+        // The format's own rule on the offending field, stated directly.
+        if (h.inEntryName) CHECK(!isValidEntryName(h.offending));
+        else CHECK(!isValidNestedSamplePath(h.offending));
+
+        // Refused by the CODEC: decode yields no manifest at all, so there is nothing
+        // for a planner to have been handed. planImport takes a PackageManifest, and
+        // decode produced none.
+        const DecodedPackage dec = decodePackage(bytes, bytes.size());
+        if (dec.status != PackageReadability::Malformed) {
+            std::printf("FAIL: %s classified %d, expected Malformed\n", h.file,
+                        static_cast<int>(dec.status));
+            ++g_fail;
+        }
+        CHECK(dec.manifest == PackageManifest{});
+        CHECK(dec.layout.empty());
+        CHECK(dec.prefixSize == 0);
+    }
+}
+
+int main() {
+    testV1FixtureDecodesToTheRecordTheShippingBuildWrote();
+    testAdditiveForwardFixtureReadsWithEveryKnownFieldIntact();
+    testRefuseFixtureIsTooNewAndStillNamesTheWriter();
+    testEveryTruncationIsMalformedNeverTooNew();
+    testEveryHostileNameIsRefusedAtDecode();
+
+    if (g_fail == 0) {
+        std::printf("package_compat_tests: all passed\n");
+        return 0;
+    }
+    std::printf("package_compat_tests: %d failure(s)\n", g_fail);
+    return 1;
+}

tests/test_package_round_trip.cpp

@@ -0,0 +1,250 @@
+// The corpus driven through both verbs — no REAPER, no framework. Where
+// test_package_compat asserts what the frozen bytes DECODE to, this file asserts what
+// the import and export verbs DO with them: the payload bytes survive a full
+// export -> import -> export, and every refusal in the corpus refuses before a planner
+// or a filesystem write is reached.
+
+#include "../src/shell/package/import_landing.h"
+
+#include <cstdint>
+#include <cstdio>
+#include <filesystem>
+#include <fstream>
+#include <string>
+#include <vector>
+
+#include "../src/core/package/bank_package.h"
+#include "../src/shell/package/export_bank.h"
+#include "../src/shell/package/package_path.h"
+#include "../src/shell/persist/session.h"
+#include "package_fixtures.h"
+
+using namespace reasampler;
+namespace fs = std::filesystem;
+
+static int g_fail = 0;
+#define CHECK(cond) do { if(!(cond)) { \
+    std::printf("FAIL line %d: %s\n", __LINE__, #cond); ++g_fail; } } while(0)
+
+static const char* kTag = "1754000000";
+static const char* kImportedBankId = "bank-imported";
+
+// --- scratch project ---------------------------------------------------------
+
+// One project directory per suite, torn down after, so no suite observes another's
+// bank folder.
+class Scratch {
+public:
+    explicit Scratch(const std::string& name) {
+        std::error_code ec;
+        dir_ = pathToUtf8(fs::temp_directory_path(ec) /
+                          utf8Path("reasampler_compat_" + name));
+        fs::remove_all(utf8Path(dir_), ec);
+        fs::create_directories(utf8Path(dir_), ec);
+    }
+    ~Scratch() {
+        std::error_code ec;
+        fs::remove_all(utf8Path(dir_), ec);
+    }
+    const std::string& projectDir() const { return dir_; }
+    std::string bankDir() const { return package::bankFolderDir(dir_); }
+    std::string importPath() const { return dir_ + "/in.rsbank"; }
+    std::string exportPath() const { return dir_ + "/out.rsbank"; }
+
+private:
+    std::string dir_;
+};
+
+static std::vector<std::uint8_t> readBytes(const std::string& path) {
+    std::ifstream f(utf8Path(path), std::ios::binary);
+    return std::vector<std::uint8_t>(std::istreambuf_iterator<char>(f),
+                                     std::istreambuf_iterator<char>());
+}
+
+static void writeBytes(const std::string& path, const std::vector<std::uint8_t>& bytes) {
+    std::ofstream f(utf8Path(path), std::ios::binary | std::ios::trunc);
+    f.write(reinterpret_cast<const char*>(bytes.data()),
+            static_cast<std::streamsize>(bytes.size()));
+}
+
+// Copies a committed fixture to the path the verb will be pointed at. Fails loudly on an
+// empty read: an unreadable corpus would otherwise let every "must refuse" suite pass.
+static bool stageFixture(const Scratch& scratch, const char* fixture) {
+    const std::vector<std::uint8_t> bytes = packageFixtureBytes(fixture);
+    if (bytes.empty()) {
+        std::printf("FAIL: fixture %s read as 0 bytes (path: %s)\n", fixture,
+                    packageFixturePath(fixture).c_str());
+        ++g_fail;
+        return false;
+    }
+    writeBytes(scratch.importPath(), bytes);
+    return true;
+}
+
+// Each entry's payload bytes, sliced out of a whole package file by its own layout.
+static std::vector<std::vector<std::uint8_t>> payloadsOf(const std::vector<std::uint8_t>& file) {
+    std::vector<std::vector<std::uint8_t>> out;
+    const package::DecodedPackage dec = package::decodePackage(file, file.size());
+    if (dec.status != package::PackageReadability::Readable) return out;
+    for (const package::PackageEntrySpan& span : dec.layout) {
+        const auto begin = file.begin() + static_cast<std::ptrdiff_t>(span.offset);
+        out.emplace_back(begin, begin + static_cast<std::ptrdiff_t>(span.length));
+    }
+    return out;
+}
+
+// --- the sequence the import verb runs, minus REAPER -------------------------
+
+static ImportLanding runImport(const Scratch& scratch, ReaSamplerSession& session,
+                               int* outBirths = nullptr) {
+    LandedFileJournal journal;
+    ImportLanding landing = landPackage(scratch.importPath(), scratch.projectDir(),
+                                        session.book(), kTag, journal);
+    if (landing.outcome != ImportOutcome::Landed) return landing;
+    int births = 0;
+    const bool applied = applyImportedBank(session.book(), kImportedBankId, landing.plan,
+                                           [&births](const model::Sample&) { ++births; });
+    CHECK(applied);
+    if (applied) journal.markIndexCommitted();
+    if (outBirths) *outBirths = births;
+    return landing;
+}
+
+// --- the round-trip anchor ---------------------------------------------------
+
+// The fixture IS the first export (written by the shipping build's own export verb), so
+// importing and re-exporting it closes export -> import -> export over frozen bytes.
+static void testV1FixtureReExportsByteIdenticalPayloads() {
+    Scratch scratch("roundtrip");
+    if (!stageFixture(scratch, "v1_shipping.rsbank")) return;
+
+    ReaSamplerSession session;
+    int births = 0;
+    const ImportLanding landing = runImport(scratch, session, &births);
+    CHECK(landing.outcome == ImportOutcome::Landed);
+    CHECK(births == 1);
+    CHECK(landing.plan.landCount == 1);
+    if (landing.plan.entries.size() != 1) { CHECK(false); return; }
+
+    const std::vector<std::vector<std::uint8_t>> sourcePayloads =
+        payloadsOf(packageFixtureBytes("v1_shipping.rsbank"));
+    CHECK(sourcePayloads.size() == 1);
+
+    // The landed file is the package's payload verbatim — the first half of the claim.
+    const std::string landed = scratch.bankDir() + "/" + landing.plan.entries[0].destFileName;
+    CHECK(readBytes(landed) == sourcePayloads[0]);
+
+    ExportRequest req;
+    req.projectDir = scratch.projectDir();
+    req.bankId = kImportedBankId;
+    req.destAbsPath = scratch.exportPath();
+    req.exportTimestamp = 1754200000;
+    const ExportOutcome out = exportBank(session, req);
+    CHECK(out.status == ExportStatus::Written);
+    CHECK(out.entriesWritten == 1);
+
+    // The second half: the re-export's payloads, byte for byte. Entry NAMES may legally
+    // differ across the trip — the importer re-spells a bank file and the exporter mints
+    // its own transport name (src/core/package/CLAUDE.md) — the payload bytes may not.
+    CHECK(payloadsOf(readBytes(scratch.exportPath())) == sourcePayloads);
+}
+
+// --- the refusals, at the verb rather than the codec -------------------------
+
+static void testRefuseFixtureRefusesTheWholeImportAndNamesTheWriter() {
+    Scratch scratch("refuse");
+    if (!stageFixture(scratch, "refuse_structural.rsbank")) return;
+
+    ReaSamplerSession session;
+    const BankBook before = session.book();
+    LandedFileJournal journal;
+    const ImportLanding landing = landPackage(scratch.importPath(), scratch.projectDir(),
+                                              session.book(), kTag, journal);
+
+    CHECK(landing.outcome == ImportOutcome::TooNew);
+    CHECK(landing.header.formatVersion == package::kPackageFormatVersion + 1);
+    CHECK(landing.header.minReaderVersion == package::kPackageFormatVersion + 1);
+    CHECK(landing.header.writerVersion == "1.9.0");
+    // Nothing planned, nothing on disk, nothing in the index.
+    CHECK(landing.plan.entries.empty());
+    CHECK(!fs::exists(utf8Path(scratch.bankDir())));
+    CHECK(session.book() == before);
+}
+
+// The same eight cuts test_package_compat classifies, driven through the verb's
+// incremental prefix reader — the one caller that can ask requiredPrefixSize for more
+// bytes than the file holds.
+static const char* kTruncationFixtures[] = {
+    "trunc_magic.rsbank",          "trunc_version_pair.rsbank",
+    "trunc_writer_semver.rsbank",  "trunc_manifest_length.rsbank",
+    "trunc_manifest_body.rsbank",  "trunc_payload_start.rsbank",
+    "trunc_payload_middle.rsbank", "trunc_one_short.rsbank",
+};
+
+static void testEveryTruncationRefusesTheImportAsMalformed() {
+    for (const char* fixture : kTruncationFixtures) {
+        Scratch scratch(std::string("trunc_") + fixture);
+        if (!stageFixture(scratch, fixture)) continue;
+
+        ReaSamplerSession session;
+        const BankBook before = session.book();
+        LandedFileJournal journal;
+        const ImportLanding landing = landPackage(scratch.importPath(), scratch.projectDir(),
+                                                  session.book(), kTag, journal);
+        if (landing.outcome != ImportOutcome::Malformed) {
+            std::printf("FAIL: %s imported as outcome %d, expected Malformed\n", fixture,
+                        static_cast<int>(landing.outcome));
+            ++g_fail;
+        }
+        CHECK(landing.plan.entries.empty());
+        CHECK(!fs::exists(utf8Path(scratch.bankDir())));
+        CHECK(session.book() == before);
+    }
+}
+
+static const char* kHostileFixtures[] = {
+    "hostile_name_dotdot.rsbank",           "hostile_name_parent_slash.rsbank",
+    "hostile_name_parent_backslash.rsbank", "hostile_name_subdir_slash.rsbank",
+    "hostile_name_drive_absolute.rsbank",   "hostile_name_unc_absolute.rsbank",
+    "hostile_path_dotdot_slash.rsbank",     "hostile_path_dotdot_backslash.rsbank",
+    "hostile_path_rooted.rsbank",           "hostile_path_drive_absolute.rsbank",
+    "hostile_path_unc_absolute.rsbank",
+};
+
+static void testEveryHostileNameIsRefusedBeforeThePlannerRuns() {
+    for (const char* fixture : kHostileFixtures) {
+        Scratch scratch(std::string("hostile_") + fixture);
+        if (!stageFixture(scratch, fixture)) continue;
+
+        ReaSamplerSession session;
+        const BankBook before = session.book();
+        LandedFileJournal journal;
+        const ImportLanding landing = landPackage(scratch.importPath(), scratch.projectDir(),
+                                                  session.book(), kTag, journal);
+        if (landing.outcome != ImportOutcome::Malformed) {
+            std::printf("FAIL: %s imported as outcome %d, expected Malformed\n", fixture,
+                        static_cast<int>(landing.outcome));
+            ++g_fail;
+        }
+        // planImport is the ONLY producer of a non-empty plan and it runs after the
+        // decode — an empty one is how "refused before any planner" is observed here.
+        CHECK(landing.plan.entries.empty());
+        CHECK(landing.plan.bankDisplayName.empty());
+        CHECK(!fs::exists(utf8Path(scratch.bankDir())));
+        CHECK(session.book() == before);
+    }
+}
+
+int main() {
+    testV1FixtureReExportsByteIdenticalPayloads();
+    testRefuseFixtureRefusesTheWholeImportAndNamesTheWriter();
+    testEveryTruncationRefusesTheImportAsMalformed();
+    testEveryHostileNameIsRefusedBeforeThePlannerRuns();
+
+    if (g_fail == 0) {
+        std::printf("package_round_trip_tests: all passed\n");
+        return 0;
+    }
+    std::printf("package_round_trip_tests: %d failure(s)\n", g_fail);
+    return 1;
+}