# Phase C+6 — re-validation

## Gate 1 — Determinism (cvar-OFF, ours)

3 fresh runs of `check -n 50000000 --stable-digest`:

| run | digest md5 |
|-----|------------|
| 1   | c6d895829b4611964978990ae1cb8a6a |
| 2   | c6d895829b4611964978990ae1cb8a6a |
| 3   | c6d895829b4611964978990ae1cb8a6a |
| C+5 baseline (cvar-OFF) | `c6d895829b4611964978990ae1cb8a6a` |

**Result**: ✅ byte-identical across 3 runs and SAME as the C+5
baseline. The Phase C+6 fix is purely an emitter-framing change (cvar
`phase_a_event_log` OFF path): the `unimplemented_exports` HashSet is
consulted only inside the `phase_a_on` guard in `call_export`. The
stub body (`stub_success`, which sets `r3 = 0`) still runs unchanged.
Therefore the cvar-OFF deterministic boot trajectory is unchanged.
Baseline digest preserved.

## Gate 2 — Phase B `image_canonical_sha256`

Phase B snapshot captured to `snap/ours/`.
`image_loaded_sha256 = ea8d160e9369328a5b922258a92113efb8d7ce3e1a5c12cc521e375985c91c18`
matches the Phase-A/B verify baseline. The fix touches only the
kernel-export shim/emitter layer — no PE image bytes modified.

## Gate 3 — Phase A matched-prefix extension (KEY METRIC)

Diffed `audit-runs/phase-c6-call-name-divergence/ours.jsonl` against
the existing `phase-c-first-divergence/phase-a/canary.jsonl`.

| chain | C+5 (pre-C+6) | C+6 (post) | Δ |
|---|---|---|---|
| canary tid=6 → ours tid=1 (main) | 102132 | **102158** | **+26** |
| canary tid=4 → ours tid=11 | 5 | 5 | 0 |
| canary tid=7 → ours tid=2 | 15 | 15 | 0 |
| canary tid=12 → ours tid=7 | 2 | 2 | 0 |
| canary tid=14 → ours tid=9 | 39 | 39 | 0 |
| canary tid=15 → ours tid=10 | (no div) | (no div) | 0 |

**Main thread matched prefix grew from 102132 to 102158. Gate 3 ✅.**

The new first-divergence at idx=102158 is `XamTaskCloseHandle`
`return_value`: canary=1, ours=0 — value divergence, NOT a call-name
divergence. That's the next Phase C+N target.

## Gate 4 — Build

```
$ cargo build --release
   Compiling xenia-kernel v0.1.0
   Compiling xenia-app v0.1.0
    Finished `release` profile [optimized] target(s) in 6.22s
```

One pre-existing dead-code warning (`walk_committed_regions`); not
introduced by this fix. Canary untouched.

## Gate 5 — Phase A determinism (emitter)

Two cvar-ON captures of the same engine binary on the same ISO,
md5-summing only deterministic fields (excluding `host_ns` AND
`guest_cycle` — both are timing-sensitive, see Stage 2's
established practice):

```
ours.jsonl     (run 1, det-fields-only)   7312446e49fa3c3149d26424832cabf4
/tmp/c6_pa_run2.jsonl (run 2, det-fields-only) 7312446e49fa3c3149d26424832cabf4
```

Byte-identical. ✅

Note: digest changes from C+5's `388d394a…` because the suppression
flips 3 events on/off in the deterministic-fields stream. Expected.

## Gate 6 — Kernel unit tests

```
$ cargo test --release -p xenia-kernel --lib
test result: ok. 145 passed; 0 failed; 0 ignored; 0 measured;
                 0 filtered out
```

1 new test added (144 → 145):

* `register_unimplemented_export_marks_set_membership` — verifies the
  new `register_unimplemented_export` API both installs the export
  func (so `call_export` finds and runs the stub) AND inserts the
  `(module, ord)` pair into `unimplemented_exports` (so the Phase A
  emitter guard suppresses events). Cross-checks the negative case:
  a normal `register_export` does NOT mark unimplemented.

Full workspace test suite (`cargo test --release --workspace`):
no regressions.

## Summary

All 6 gates pass. Phase A main matched prefix grew from 102132 to
102158 (+26 events). One class-E (Phase A coverage gap) engine bug
fixed: ours's emitter injected 3 spurious events
(`import.call`/`kernel.call`/`kernel.return`) for
`IoDismountVolumeByFileHandle` because canary's syscall-thunk path
for table-entry-only exports never reaches `Trampoline` and emits
nothing. New `register_unimplemented_export` API in `state.rs` lets
us mark such exports for Phase A suppression while keeping their
stub body execution intact. Cvar-OFF inert.

Diff-tool unchanged. Canary unchanged.

Next divergence: **XamTaskCloseHandle return value at
tid_event_idx=102158** (canary=1, ours=0 — value divergence). Phase
C+7 target.