fix(csharp): copy-on-read frozen binding arrays in namespace-siblings

[mann1x]

Summary

scope-extractor.ts freezes per-name binding arrays via frozenBindings.set(name, Object.freeze(refs.slice())) (line 180). When populateCsharpNamespaceSiblings later reads back an existing entry via scopeBindings.get(name) ?? [] and tries to existing.push(...) on it, the frozen reference throws

TypeError: Cannot add property N, object is not extensible
    at Array.push (<anonymous>)
    at Object.populateCsharpNamespaceSiblings [as populateNamespaceSiblings]
      (.../csharp/namespace-siblings.js:321:26)
    at runScopeResolution (.../scope-resolution/pipeline/run.js:113:18)
    ...
  Phase 'scopeResolution' failed

…which abandons scope resolution for the entire repo (the index is never produced). The populator's leading comment says "indexes.bindings is typed ReadonlyMap<...> but is a plain Map at runtime; mutating here is the established pattern" — that's true for the outer Map, but the inner per-name arrays are nonetheless frozen by the extractor, so the established pattern is silently broken at three sites.

Reproduction

Triggered when a file locally declares a class with the same simple name as a class in a sibling namespace imported via using. Hit live on the PersistentWindows real-world WinForms repo (large mix of .Designer.cs + namespaced classes); also hit on smaller mixed-namespace C# codebases.

Minimal fixture added under test/fixtures/cross-file-binding/csharp-frozen-binding-collision/:

• Models/User.cs declares Collision.Models.User
• App/Program.cs imports using Collision.Models; AND locally declares class User in Collision.App — the local declaration causes scope-extractor to populate (and freeze) User in the Module scope's bindings; the populator's namespace-import path then attempts to push Collision.Models.User into the same frozen array.

Fix

Spread to a fresh mutable copy on read at all three sites in populateCsharpNamespaceSiblings:

- const existing = scopeBindings.get(name) ?? [];
+ const existing: BindingRef[] = [...(scopeBindings.get(name) ?? [])];

When the populator hits a name pre-populated by the extractor, it now appends to a fresh array and writes that back, replacing the frozen entry in the per-scope Map. Origin precedence (local shadows namespace) is preserved by the existing csharpMergeBindings ordering (see csharp-hooks.test.ts).

Three sites fixed:

• populateCsharpNamespaceSiblings using-static loop (origin: 'import')
• populateCsharpNamespaceSiblings namespace-import loop (origin: 'namespace')
• populateCsharpNamespaceSiblings cross-namespace bucket loop (third namespace-injection site)

Verification

• npx tsc --noEmit clean
• npx vitest run test/integration/resolvers/csharp.test.ts test/unit/scope-resolution/csharp/ test/unit/named-bindings/csharp.test.ts → 5 test files / 282 tests / 0 fail (3 of those are the new regression test + 279 existing).
• Pre-fix beforeAll of the new test rejects with Phase 'scopeResolution' failed: Cannot add property N, object is not extensible. Post-fix all three test cases pass: scope resolution completes, both User declarations are detected, and new User() inside Program.Run() resolves to the local Collision.App.User (origin:local shadows origin:namespace).

Risk / rollback

Minimal — purely a copy-on-read tweak in a populator that already documented its intent to mutate the per-name arrays. Behavior is unchanged for callers that don't pre-populate the same name. The Object.freeze upstream in scope-extractor.ts is left in place; if a future change wants to enforce true immutability throughout, this is the right starting point because it makes the freeze contract honest at the populator boundary instead of silently broken.

Rollback: revert the commit; the upstream behavior degrades back to crashing on collision.

Test plan

• npx tsc --noEmit in gitnexus/
• Full C# test suite green (integration + unit + named-bindings)
• New regression test fails before fix, passes after
• Optional: maintainer to run on a wider corpus

[vercel]

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[magyargergo]

I just merged, i think, a fix, for it. Could you please check #1082 ?

[magyargergo]

We could use your test fixture to test it against.

[mann1x]

Wow almost in parallel!
Let me check it out

[mann1x]

Confirmed, it works and it's great, real major improvement!

  ┌─────────────────────────────────────────────┬────────────────────────┬────────────────────────────────┬──────────────┐
  │                                             │ Before (PR #1083 fork) │ After (PR #1082 upstream/main) │      Δ       │
  ├─────────────────────────────────────────────┼────────────────────────┼────────────────────────────────┼──────────────┤
  │ Cannot add property … not extensible errors │ 0 (also fixed)         │ 0                              │ —            │
  ├─────────────────────────────────────────────┼────────────────────────┼────────────────────────────────┼──────────────┤
  │ Other freeze-related crashes                │ 0                      │ 0                              │ —            │
  ├─────────────────────────────────────────────┼────────────────────────┼────────────────────────────────┼──────────────┤
  │ Nodes                                       │ 1025                   │ 1113                           │ +88 (+8.6%)  │
  ├─────────────────────────────────────────────┼────────────────────────┼────────────────────────────────┼──────────────┤
  │ Edges                                       │ 1715                   │ 2987                           │ +1272 (+74%) │
  ├─────────────────────────────────────────────┼────────────────────────┼────────────────────────────────┼──────────────┤
  │ Clusters                                    │ 28                     │ 39                             │ +11          │
  ├─────────────────────────────────────────────┼────────────────────────┼────────────────────────────────┼──────────────┤
  │ Flows                                       │ 25                     │ 97                             │ +72 (+288%)  │
  ├─────────────────────────────────────────────┼────────────────────────┼────────────────────────────────┼──────────────┤
  │ Wall time                                   │ 5.6 s                  │ 8.1 s                          │ +2.5 s       │
  └─────────────────────────────────────────────┴────────────────────────┴────────────────────────────────┴──────────────┘

Closing this and opening a small PR for the fixture-only.