pgxp: emit hook macros + dual build targets + flavor-namespaced caches (phase 2)

Emitter side of the value-propagation engine (ENHANCEMENTS.md G1.10):

- recompiler/src/pgxp_hook_emitter.{h,cpp} (new, in the codegen-hash
  surface): ONE hook grammar shared by BOTH emitters, wrapping loads/
  stores/COP2 transfers and precision-carrying ALU ops (moves, add/sub,
  or-merge, shifts, LUI, HI/LO, muldiv) with PGXP_*() macros. Clobberable
  sources are captured into locals before the statement. Precision-
  destroying ops (AND/XOR/SLT/...) are deliberately unhooked - validate-
  on-read drops their stale shadows for free.
- code_generator.cpp: central append in translate_instruction; LWC2/SWC2
  emissions capture the RAW loaded/stored word (a masked GTE register
  write must validate against the word as loaded).
- strict_translator.cpp: translate() wraps translate_impl()'s c_code with
  the shared grammar; deferred load-delay variants hook the psx_ldd temp.
- BIOS regenerated, fingerprints verified CHANGED (SCPH1001 + OpenBIOS;
  42.6k/12.2k macro sites). Base runtime + 33/33 tests green against it.
- Gating: macros expand only under -DPSX_PGXP=1. runtime.cmake grows a
  PGXP option on psxrecomp_add_runtime_target (defines PSX_PGXP=1 +
  PSX_OVERLAY_FLAVOR=2, _pgxp exe suffix) and PSX_PGXP_VARIANT to build
  the sibling target from the same generated tree (framework runtime +
  game wrapper). No ABI version bump needed: the appended PGXPHooks
  table is NULL-tolerant and the flavor half of the ABI tag rejects any
  host/DLL flavor mix.
- Shard caches: flavor folded into the cache tag (cg<V>_<hash>_gc<hash>
  _f<flavor>) in overlay_loader.c + compile_overlays.py so base and pgxp
  caches never share a directory; compile_overlays.py passes
  -DPSX_PGXP=1 when flavor bit 2 is set; overlay preamble forwards
  psx_pgxp_* through the table. PSX_OVERLAY_CODEGEN_VER 9 -> 10.
- Env overrides PSX_GEOMETRY_CORRECTION / PSX_PERSPECTIVE_TEXTURING /
  PSX_PGXP_CPU_MODE (validation path: free-running headless boots arm
  from the first vertex); census grew produced/swc2_stores and the pgxp
  verb reports suppress/active gate state.

Validated: PSXRecomp_pgxp.exe boots the recompiled BIOS with hooks armed
(engine active, per-vertex lookups flowing; the BIOS shell has no RTPS
content so produced=0 there is correct - coverage measurement moves to a
3D title in phase 3).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

runtime/include/overlay_api.h

@@ -86,6 +86,13 @@
  *      model participation with queue-safe guard/hysteresis policy. */
 /* v21: ws_angle_widen forwarder for exact, aspect-scaled 12-bit terrain
  *      frustum half-angle constants. */
+/* (PGXP, no version bump): OverlayCallbacks grew an appended-last PGXPHooks
+ *      table pointer (pgxp_hooks.h). Only pgxp-flavour shards (compiled with
+ *      -DPSX_PGXP=1, PSX_OVERLAY_FLAVOR_PGXP set) reference the psx_pgxp_*
+ *      forwarders, and the flavor half of the ABI tag already rejects any
+ *      host/DLL flavor mix — base-flavour DLLs and hosts are untouched, so
+ *      the version stays. The emit-content change (PGXP_*() macros in all
+ *      generated C) is covered by the codegen hash + CODEGEN_VER below. */
 #define PSX_OVERLAY_ABI_VERSION 21
 
 /* Process-lifetime overlay candidate capacity.  Every accepted manifest F
@@ -113,6 +120,12 @@
 #define PSX_OVERLAY_FLAVOR 0
 #endif
 
+/* Flavor bits (compose bitwise; base = 0):
+ *   1 — widescreen variant codegen
+ *   2 — PGXP precision shadowing (-DPSX_PGXP=1 objects; pgxp_hooks.h) */
+#define PSX_OVERLAY_FLAVOR_WIDESCREEN 1
+#define PSX_OVERLAY_FLAVOR_PGXP       2
+
 /* Combined tag exported by overlay_abi() and checked by the loader. */
 #define PSX_OVERLAY_ABI_TAG \
     ((int)((PSX_OVERLAY_ABI_VERSION & 0xFFFF) | ((PSX_OVERLAY_FLAVOR & 0xFFFF) << 16)))
@@ -139,8 +152,11 @@
  *      masked-16-bit screen-X, and depth cull emits.
  *   7: + configured side-plane normal-X (plane_nx) cull emit.
  *   8: + configured per-primitive bound-load (xclip) cull emit.
- *   9: + full-word-guarded object/model participation compare emit. */
-#define PSX_OVERLAY_CODEGEN_VER 9
+ *   9: + full-word-guarded object/model participation compare emit.
+ *  10: + PGXP dataflow-shadowing PGXP_*() macro emission at loads/stores/
+ *      COP2 transfers/precision-carrying ALU ops (pgxp_hooks.h; no-ops in
+ *      base-flavour objects, real hooks under -DPSX_PGXP=1). */
+#define PSX_OVERLAY_CODEGEN_VER 10
 
 /* Auto codegen hash (generated by hash_codegen.cmake from the recompiler codegen
  * sources). Folded into the cache PATH next to cg<N> (gcc/<arch-abi>/cg<N>_<hash>/)