# Phase C+23 broad-impact assessment (2026-05-18)

## Resolved

- **D-NEW-2 (C+17 catalog)** — KeWait timeout `wait.begin.timeout_ns`
  on canary tid=12 → ours tid=7 idx=3. Was 429466729600 (broken
  positive sign-extension); now -30000000 matching canary exactly.
  Sister chain advances 3 → 4.

## Advanced

- **`addis` opcode semantics across the entire CPU interpreter**.
  Any place in any guest binary using `lis`/`addis` with a negative
  immediate that flows into a 64-bit `std`, `mr`, `orx`, or anything
  else that propagates the full GPR value will now produce
  canary-equivalent behavior. The KeWait timeout was just the first
  observable symptom in Sylpheed's cold-vs-cold trajectory.

## Persisted (no change)

- Main matched-prefix tid=6→1 = **104,607** (the C+22 scheduler-
  determinism asymmetry is unaffected by this fix).
- Sister chains tid=4→11 (11), tid=7→2 (32), tid=14→9 (41),
  tid=15→10 (16).
- Phase B `image_canonical_sha256 = ea8d160e9369328a5b922258a92113ef
  b8d7ce3e1a5c12cc521e375985c91c18`.
- Kernel tests 204 (unchanged — no kernel-side code change).

## NEW

- **D-NEW-2.1 (idx=4 sister chain canary tid=12 → ours tid=7)**:
  `KeWaitForSingleObject` return value canary=258 (TIMEOUT) vs
  ours=0 (SUCCESS). Same C+20/C+22 family — scheduler-determinism;
  ours's monolithic-thread runner allows the wait to return
  SUCCESS where canary's contended scheduler lets the 30 ms timeout
  elapse with no signaler. Out of scope for this phase; same
  parallel scheduler-determinism track recommended in C+22.

- **CPU correctness probe**: opportunity for a low-key audit of
  every "32-bit ABI defensive truncation" in
  `xenia-cpu/src/interpreter.rs` for other ops that legitimately
  need 64-bit sign-extension at the producer rather than truncation.
  Quick mental scan suggests `addis` was likely the only such case;
  `addi` already extends via `simm16 as i64 as u64`, `ori`/`oris`
  are pure 64-bit OR. Not a blocking concern.

## Test count delta

| crate         | pre-C+23 | post-C+23 | delta |
|---------------|----------|-----------|-------|
| xenia-cpu     | 288      | 291       | +3    |
| xenia-kernel  | 204      | 204       | 0     |

## Cold-stable digest delta

| baseline               | pre-C+23                          | post-C+23                         |
|------------------------|-----------------------------------|-----------------------------------|
| ours-cold det-fields   | e1dfcb1559f987b35012a7f2dc6d93f5  | 23cf4c4cbf61a577caa4118ab2308ba6  |
| Phase B image_canonical| ea8d160e9369…                     | ea8d160e9369…  (UNCHANGED)        |

3× ours-cold runs all yield the new digest. Determinism preserved.