# Phase C+13 broad-impact assessment

## Resolved

| event | before | after |
|---|---|---|
| Main idx 103862 `NtCreateFile(game:\\dat\\files.tbl)` | ours=`0x00000000` (synth-success) / canary=`0xc0000034` | ours=`0xc0000034` matches canary bit-for-bit |

## Advanced

| metric | before | after | delta |
|---|---|---|---|
| Main cold-vs-cold matched prefix (canary tid=6 → ours tid=1) | 103,862 | 104,574 | **+712 events** |
| Stable digest `imports` | 40,447 | 40,390 | -57 |
| Stable digest `instructions` | 50,000,002 | 50,000,007 | +5 |

`imports -57` is the population of previously-masked missing-disc-file
probes: each one used to emit a synth-success kernel.call/return pair
plus an `import.call`, ours now emits just a NOT_FOUND kernel.return.
Net 57 import-call slots freed = ~28 distinct missing-file paths that
the boot validator now sees as NOT_FOUND.

## Persisted (sister chains, all unchanged)

| canary_tid | ours_tid | matched | notes |
|---|---|---|---|
| 4  | 11 | 9      | no divergence in compared events |
| 7  | 2  | 29     | no divergence in compared events |
| 12 | 7  | 2      | pre-existing KeWaitForSingleObject TIMEOUT/SUCCESS |
| 14 | 9  | 39     | pre-existing XAudio init divergence |
| 15 | 10 | 15     | no divergence in compared events |

No sister-chain regression. The fix is scoped to `open_vfs_file`'s
disc-path arm; sister tids don't touch this code path during their
captured windows.

## NEW (surfaced by the fix)

| location | observation |
|---|---|
| Main idx 104574 | Ordinal-of-call mismatch: canary does **two** sequential `RtlEnterCriticalSection` (104571, 104574); ours does one `Enter` then `Leave`. Likely an error-handling path in Sylpheed's boot validator that takes a nested lock on disc-file NOT_FOUND. |

This is the expected pattern: scoping the synth-empty surfaces the
code branch that handles missing disc files honestly. The new
divergence is at the next layer of the boot validator's error-path
logic and becomes the Phase C+14 target.

## Risk: did anything regress in non-cold scenarios?

- **Kernel unit tests**: 177 → 181 pass; no failures. The new
  `nt_create_file_non_disc_prefix_missing_still_synthesizes` test
  proves the legacy synth-empty path is preserved for non-disc
  prefixes (i.e. writable system partitions).
- **Phase B image hash**: unchanged. The fix doesn't touch image
  loading.
- **Lockstep goldens**: `--stable-digest` 3× determinism PASS; no
  jitter introduced. The C+12 baseline digest was already a
  stable-mode reference, so the new digest just becomes the C+13
  baseline.

## Summary

One divergence Resolved (idx 103862). +712 events Advanced on the
main chain. Zero sister regressions. One NEW divergence at idx
104574 — a higher-quality target (error-handling path divergence)
than a synth-empty masked divergence.