M5.5: this-flow indirect-dispatch resolution via vptr-write inference

Closes the dominant case M5 could not resolve — `lwz vt, off(this);
lwz fn, slot(vt); mtctr; bcctrl` (real C++ dispatch). Implements
class-membership inference using constructor-side vptr writes as an
oracle for which vtables can land at each offset.

## Algorithm

Phase 1 — vptr-write scan: walk every function with the existing
lis+addi register tracker. When `stw rA, off(rB)` writes a known M3
vtable address into off(rB), record `(vtable_addr, vptr_offset,
writer_pc, writer_function)` as a constructor-side vptr write.

Phase 2 — invert by offset: `vtables_by_offset[off] = {V : V written
at off in any ctor}`.

Phase 3 — dispatch detection: from each `bcctrl LK=1`, walk back
≤16 instructions looking for the canonical chain. Bail on register
clobber, branch, or label (basic-block) boundary.

Phase 4 — edge emission: for `(dispatch_pc, vptr_off, slot)`, emit one
`xrefs.kind='ind_call'` row per vtable V where:
  - `vtables_by_offset[vptr_off]` contains V, AND
  - `V.length > slot` (V actually has a method at that slot)

Multi-candidate sites (the common case at offset 0) are an
over-approximation; downstream queries filter to single-candidate sites
for high confidence:
  `WHERE candidate_count=1` in `indirect_dispatch_sites`.

## Schema

NEW TABLES:
- `vptr_writes(writer_pc, vtable_address, vptr_offset, writer_function)`
- `indirect_dispatch_sites(dispatch_pc PK, vptr_offset, slot, candidate_count)`
- `indirect_dispatch_candidates(dispatch_pc, vtable_address, method_address)`

NEW INDICES on vtable_address / vptr_offset / method_address /
(vptr_offset, slot) for fast joins.

## Sylpheed yield

- 567 vptr writes / 214 vtables / 29 offsets (offset 0 = 88%).
- 6,842 dispatch sites resolved: 97 single-candidate (high-confidence) +
  6,745 multi-candidate.
- 687,963 ind_call xref rows.
- 2,746 newly-reachable functions via v_indirect_reachability_from_entry
  (compared to 0 with M5 alone).
- Audit-009 cluster: functions including 0x823BC9E0, 0x823BC290,
  0x823BC5A0, 0x823BB158 newly reachable — actionable for the
  renderer-plateau hunt.

Tests 640→649 (+4 ind_dispatch_typed unit tests + 5 from tighter golden
expansion). Schema golden + write_analysis_results signature updated.

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

crates/xenia-analysis/tests/db_schema_golden.rs

@@ -107,7 +107,7 @@ fn db_schema_matches_expected_columns() {
         w.write_base(&info).expect("write_base");
         w.ingest_instructions(&pe, &info, &func_analysis, &labels)
             .expect("ingest_instructions");
-        w.write_analysis_results(&pe, &info, &func_analysis, &labels, &xrefs, &[], &[], &[])
+        w.write_analysis_results(&pe, &info, &func_analysis, &labels, &xrefs, &[], &[], &[], None)
             .expect("write_analysis_results");
         w.create_sql_views().expect("create_sql_views");
     }
@@ -232,6 +232,23 @@ fn db_schema_matches_expected_columns() {
             ("slot", "BIGINT"),
             ("function_address", "BIGINT"),
         ]),
+        ("indirect_dispatch_sites", &[
+            ("dispatch_pc", "BIGINT"),
+            ("vptr_offset", "BIGINT"),
+            ("slot", "BIGINT"),
+            ("candidate_count", "BIGINT"),
+        ]),
+        ("indirect_dispatch_candidates", &[
+            ("dispatch_pc", "BIGINT"),
+            ("vtable_address", "BIGINT"),
+            ("method_address", "BIGINT"),
+        ]),
+        ("vptr_writes", &[
+            ("writer_pc", "BIGINT"),
+            ("vtable_address", "BIGINT"),
+            ("vptr_offset", "BIGINT"),
+            ("writer_function", "BIGINT"),
+        ]),
         ("xrefs", &[
             ("source", "BIGINT"),
             ("target", "BIGINT"),