fix: preserve concrete type identity in selected map keys

[picatz]

Summary

• Preserve concrete interface key types in direct and helper map write/delete matching: int(1), int64(1), and defined types are distinct; aliases retain Go identity.
• Resolve wrapped helper key parameters across nesting without rewriting SSA or changing value-summary substitution.
• Normalize supported scalar conversions, with a representability fast path for ordinary integers.
• Keep map-range behavior, alias policy, finite summary reduction, and nested event composition unchanged.

Precision boundary

Native int, uint, and uintptr values outside the range common to 32- and 64-bit targets remain unknown because this SSA layer does not provide target sizes. Three same-large-native-key controls are explicitly conservative: baseline 0 findings, candidate 1, semantic expectation 0. Fractional/out-of-range float-to-int and integer-to-string conversions remain weak.

The targeted 77-case behavioral matrix corrects 43 baseline fixture results: 22 missed flows and 21 overreports. The three native-width controls are separate. These synthetic counts are not a prevalence estimate or global soundness claim.

Validation

All gates pass on frozen head cbd9cc8a236e9997b8bfbbec2088f521d214f1e9:

• All eight hosted checks: full builds/tests on patched Go 1.26.9 and 1.27.2; both existing scoped race jobs; vet, formatting, Staticcheck, and govulncheck.
• All 15 pinned corpus snapshots unchanged; scoreboard byte-identical at 8 TP, 5 known FN, 0 FP.
• 77 behavioral cases, 21 scalar cases, and three labeled native-width controls; repeated full diagnostics/evidence and attribution checks.
• Exact diagnostic/evidence parity on 17 unchanged valid-SSA helper fixtures; existing finite/reference, cursor-boundary and map-range coverage passes.
• Independent review passed 45 behavioral and 21 scalar cases. The final integer-fit delta received a separate source review and passed 11,099 comparisons against the preceding normalization function.
• All 362 final source blobs verified against the remote tree; complete premerge source/evidence archive retained.

Allocation measurements

Complete helper-key queries exclude SSA construction. Three allocation repetitions agree:

• String: 600 B/12 allocations → 552 B/7
• Int64 and interface-int64: 546 B/8 → 552 B/7
• Wrapped parameter: 504 B/8 → 552 B/7
• Nested wrapped parameter: 1176 B/14 → 1584 B/16
• Numeric wrapping: 477 B/6 → 648 B/11

The last three include newly corrected result/parameter behavior. Initial unoptimized int64 matching used 1160 B/29; the reviewed fast path removes that overhead. Existing bounded string-helper shapes save 48 B/5 allocations per query. No shared-host timing claim is made.

Inherited nested conditional clear/delete, nested write-then-delete, uncertain-map alias, and helper range limitations remain outside this correction.