[Sylvester Kaczmarek (sylvesterkaczmarek)]

Summary

Fixes #12506.

Keep scalar initializer lookup bound to the instantiated scalar, including aliases and inherited constructors. Resolve initializer parameters with the active template mapper instead of reusing an unresolved declaration-level parameter. Existing assignability rules are unchanged.

Add regressions for the reported assignment, exact scalar identity, multiple instantiations in either order, default arguments, scalar/constructor aliases, inherited initializers, and invalid argument types. Include a compiler changelog entry. No dependency or lockfile changes.

Validation

• Full workspace pnpm test --maxWorkers=4: 10,670 passed, 25 skipped across 500 passing files and one skipped file.
• Compiler end-to-end suite: 45 passed.
• Full pnpm build: 48 tasks successful, including engineering type checks and compiler external-signature generation.
• Full formatter and type-aware lint passed, with zero lint warnings or errors.
• Before the fix, the focused three-file run had 14 failed and 33 passed; the same run passes all 47 tests with the fix. Expanded related coverage passed 772 tests.
• Independent pre-submission review found no actionable defects; its 888 focused repository tests and 30 additional probes passed.
• The built CLI accepts the exact issue reproduction and still rejects Test<string>.from(123) through a scalar alias with the expected invalid-argument diagnostic.

Validated on macOS arm64 with the repository-pinned Node 26.5.1 and pnpm 11.10.0. Full validation ran in an identical-source isolated checkout to avoid unrelated home-directory module resolution. Source hashes match the submitted files. Hosted CI and maintainer review remain pending.

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