chore: add migration/ bundle for cross-machine setup

Bundles state that lives OUTSIDE the xenia-rs repo so a fresh clone on
another machine can be brought up to identical configuration via
migration/setup.sh:

  - claude-memory/             ~/.claude/projects/-home-fabi-RE-Project-Sylpheed/memory/
                               (103 files, 1.1 MB - MEMORY.md + every
                                project_xenia_rs_*.md from audits
                                addis_signext through audit-058)
  - project-root/dot-claude/   <project-root>/.claude/settings.json
                               (Stop hook + permissions)
  - project-root/ppc-manual/   <project-root>/ppc-manual/
                               (PowerPC reference docs, 397 files, 3.7 MB)
  - project-root/run-canary.sh <project-root>/run-canary.sh
  - README.md                  Human-readable setup checklist
  - setup.sh                   Idempotent installer (also reclones
                               xenia-canary at pinned HEAD 6de80dffe)
  - MANIFEST.md                Per-file mapping + per-file-not-bundled
                               restoration recipe

Excluded from bundle (not shippable via git):
  - Sylpheed ISO (7.8 GB; copyright; manual copy required)
  - sylpheed.db (395 MB; regenerable from XEX via analysis tooling)
  - target/ build artifacts (rebuild on target)
  - audit-runs probe firehoses (.log/.stdout/.stderr ~11 GB; rerun if needed)
  - audit-runs memory dumps (.bin ~4.5 GB; rerun audit-026/027/029 if needed)
  - xenia-canary checkout (setup.sh reclones from
    git.mc02.dev/fabi/Xenia-Canary.git at HEAD 6de80dffe)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

migration/project-root/ppc-manual/fpu/fmsubx.md

@@ -0,0 +1,135 @@
+# `fmsubx` — Floating Multiply-Subtract
+
+> **Category:** [Floating-Point](../categories/fpu.md) · **Form:** [A](../forms/A.md) · **Opcode:** `0xfc000038`
+
+<!-- GENERATED: BEGIN -->
+
+## Assembler Mnemonics
+
+| Mnemonic | XML entry | Flags | Description |
+| --- | --- | --- | --- |
+| `fmsub` | `fmsubx` | — | Floating Multiply-Subtract |
+| `fmsub.` | `fmsubx` | Rc=1 | Floating Multiply-Subtract |
+
+## Syntax
+
+```asm
+fmsub[Rc] [FD], [FA], [FC], [FB]
+```
+
+## Encoding
+
+### `fmsubx` — form `A`
+
+- **Opcode word:** `0xfc000038`
+- **Primary opcode (bits 0–5):** `63`
+- **Extended opcode:** `28`
+- **Synchronising:** no
+
+| Bits | Field | Meaning |
+| --- | --- | --- |
+| 0–5 | `OPCD` | primary opcode (59 or 63) |
+| 6–10 | `FRT` | destination FPR |
+| 11–15 | `FRA` | source A FPR |
+| 16–20 | `FRB` | source B FPR |
+| 21–25 | `FRC` | source C FPR (multiplier for madd-style ops) |
+| 26–30 | `XO` | extended opcode (5 bits) |
+| 31 | `Rc` | record-form flag (updates CR1) |
+
+## Operands
+
+| Field | Role | Description |
+| --- | --- | --- |
+| `FA` | fmsubx: read | Source A floating-point register (`fr0`–`fr31`). |
+| `FC` | fmsubx: read | Source C floating-point register (for madd-style ops). |
+| `FB` | fmsubx: read | Source B floating-point register. |
+| `FD` | fmsubx: write | Destination floating-point register. |
+| `CR` | fmsubx: write (conditional) | Condition-register update. When `Rc=1`, CR field 0 (or CR6 for vector compares, CR1 for FPU) is updated from the result. |
+| `FPSCR` | fmsubx: write | Floating-Point Status and Control Register. |
+
+## Register Effects
+
+### `fmsubx`
+
+- **Reads (always):** `FA`, `FC`, `FB`
+- **Reads (conditional):** _none_
+- **Writes (always):** `FD`, `FPSCR`
+- **Writes (conditional):** `CR`
+
+## Status-Register Effects
+
+- `fmsubx`: **CR1** ← FPSCR[FX, FEX, VX, OX] when `Rc=1`.; **FPSCR** updated per IEEE-754 flags (FX, FEX, FPRF, FR, FI, exceptions).
+
+## Operation (pseudocode)
+
+```
+FRT <- (FRA × FRC) − FRB
+```
+
+## C Translation Example
+
+```c
+/* C translation: the xenia-rs interpreter arm below in           */
+/* Implementation References is the authoritative semantic        */
+/* snapshot. Translate it line-by-line:                            */
+/*   - ctx.gpr[N]  -> r[N]       (or f[]/v[] for FPRs/VRs)        */
+/*   - mem.read_u*/write_u* -> mem_read_u*_be / mem_write_u*_be   */
+/*   - ctx.update_cr_signed(fld, v) -> update_cr_signed(fld, v)   */
+/*   - ctx.xer_ca / xer_ov / xer_so -> xer.CA / xer.OV / xer.SO   */
+/* The Register Effects and Status-Register Effects tables above  */
+/* enumerate every side effect a faithful translation must emit.  */
+```
+
+## Implementation References
+
+**`fmsubx`**
+- xenia-canary XML: [`tools/ppc-instructions.xml` — search for `mnem="fmsubx"`](../../xenia-canary/tools/ppc-instructions.xml)
+- xenia-canary emit: [`src/xenia/cpu/ppc/ppc_emit_fpu.cc:205`](../../xenia-canary/src/xenia/cpu/ppc/ppc_emit_fpu.cc#L205)
+- xenia-rs opcode: [`crates/xenia-cpu/src/opcode.rs:28`](../../xenia-rs/crates/xenia-cpu/src/opcode.rs#L28)
+- xenia-rs decoder: [`crates/xenia-cpu/src/decoder.rs:927`](../../xenia-rs/crates/xenia-cpu/src/decoder.rs#L927)
+- xenia-rs interpreter: [`crates/xenia-cpu/src/interpreter.rs:2666-2678`](../../xenia-rs/crates/xenia-cpu/src/interpreter.rs#L2666-L2678)
+<details><summary>xenia-rs interpreter body (frozen snapshot)</summary>
+
+```rust
+        PpcOpcode::fmsubx => {
+            // PPCBUG-203: missing VXISI on sub step.
+            let a = ctx.fpr[instr.ra()];
+            let c = ctx.fpr[instr.rc()];
+            let b = ctx.fpr[instr.rb()];
+            fpscr::check_invalid_mul(ctx, a, c);
+            fpscr::check_invalid_fma_add(ctx, a, c, b, true);
+            let result = a.mul_add(c, -b);
+            ctx.fpr[instr.rd()] = result;
+            fpscr::update_after_op(ctx, result, a.is_finite() && b.is_finite() && c.is_finite());
+            if instr.rc_bit() { update_cr1_from_fpscr(ctx); }
+            ctx.pc += 4;
+        }
+```
+</details>
+
+<!-- GENERATED: END -->
+
+## Special Cases & Edge Conditions
+
+- **Single rounding step.** `fmsub` computes `(FRA × FRC) − FRB` with one rounding at the end. xenia-rs implements this as `a.mul_add(c, -b)`, which is a true FMA on hosts that have hardware support and a software FMA on those that don't.
+- **Subtle: negate-then-FMA.** Negating `b` before passing to FMA matters for sign of zero and overflow. `(+0×+0) − (+0)` = `+0` in round-to-nearest, but `(+0×+0) − (−0)` = `+0` (the negation flips it before the FMA). Standard IEEE rules apply.
+- **Operand order.** Assembler: `FD, FA, FC, FB`.
+- **Invalid operations.** `0×∞ − finite` → `VXIMZ`; same-signed infinity collision (e.g. `(+∞×+1) − (+∞)`) → `VXISI`. Quiet NaN result with `FPSCR[VX, FX]`.
+- **FPSCR side effects.** Hardware updates `FPRF`, `FR`, `FI`, `FX`, `OX`, `UX`, `XX`, `VXIMZ`, `VXISI`, `VXSNAN`. xenia-rs does not update FPSCR (xenia quirk).
+- **`Rc=1` (`fmsub.`)** copies `FPSCR[FX, FEX, VX, OX]` into CR1.
+- **NaN propagation.** Quiet-NaN result for any NaN operand; signalling NaNs are quietened.
+- **Use case.** Newton-Raphson refinement of reciprocal estimates: `x_new = x*(2 - d*x) = -((d*x) - 2)` uses `fnmsub`, but `fmsub` shows up wherever `(a*c) - b` appears (residuals, error correction).
+- **Denormal flush.** Xenon boots with `FPSCR[NI]=1`; xenia uses host IEEE behavior.
+
+## Related Instructions
+
+- [`fmsubsx`](fmsubsx.md) — single-precision sibling.
+- [`fmaddx`](fmaddx.md), [`fnmaddx`](fnmaddx.md), [`fnmsubx`](fnmsubx.md) — other fused multiply-add variants.
+- [`fmulx`](fmulx.md), [`fsubx`](fsubx.md) — non-fused decomposition (two rounding steps).
+- [`fresx`](fresx.md), [`frsqrtex`](frsqrtex.md) — reciprocal helpers refined by fused multiply-subtracts.
+- [`fnegx`](fnegx.md) — sign flip (the bit-pattern op behind `-FRB` in xenia's implementation).
+
+## IBM Reference
+
+- [AIX 7.3 — `fmsub` (Floating Multiply-Subtract)](https://www.ibm.com/docs/en/aix/7.3.0?topic=set-fms-fmsub-floating-multiply-subtract-instruction)
+- [PowerISA v2.07B, Book I, Chapter 4 — Floating-Point Processor](https://openpowerfoundation.org/specifications/isa/).