build: Module boundaries were preserved in package output

[cmath10]

The build emitted implementations such as assertions-HASH.mjs behind public entrypoint facades. Preserve source module boundaries so assertions.mjs and the other named modules contain their implementations and serve as shared dependencies in both ESM and CJS output.

preserveModulesRoot keeps paths relative to src. Internal modules are emitted as separate, stably named files; package exports remain unchanged.

The packed consumer check now rejects hashed runtime chunks, verifies direct imports through the public assertions and predicates modules, and checks that every assertion has the same identity through the root and assertions entrypoints.

Validation: yarn lint, yarn typecheck, yarn test (235 tests, 100% coverage), yarn build, and packed consumer checks for ESM/CJS, strict NodeNext/Bundler types, and tree shaking. Packed consumer checks ran outside the sandbox because child npm processes were blocked with EPERM.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (3e47539) to head (2c32c20).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main        #7   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           11        11           
  Lines          851       851           
  Branches       191       191           
=========================================
  Hits           851       851           

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