Preserve nested runtime config policies

[rogerchappel]

Summary

• preserve effective bargeIn and halfDuplex siblings during partial updateConfig calls
• add a regression that proves disabled barge-in and cancellation remain disabled during qualifying speech
• document incremental nested merge semantics in the API, state-machine contract, README, and changelog

Commits

• 25dc95f test: cover incremental nested config updates
• 4086211 fix: preserve nested runtime config policies
• de32ce4 docs: define incremental config update semantics

Verification

• node --test test/core-state-engine.test.js (regression failed before the fix, then passed: 11 tests)
• npm ci --ignore-scripts --no-audit --no-fund
• npm run release:check (48 tests, syntax, typecheck, build, fixture smoke, installed-package/import and pack verification)
• npm run check
• npm run package:smoke
• git diff --check origin/main...HEAD

All commit authors and committers are exactly Roger Chappel <miscanalysis@gmail.com>.

[rogerchappel]

Automated merge note

Triage class: auto-merge

Summary: Preserves effective nested bargeIn and halfDuplex policy siblings during partial runtime configuration updates, with focused regression coverage and documentation (6 files, +66/-1).

Checks run: GitHub CI verify — COMPLETED/SUCCESS; originating worker ran the focused regression, npm ci --ignore-scripts --no-audit --no-fund, npm run release:check (48 tests, syntax, typecheck, build, fixture smoke, installed-package/import and pack checks), npm run check, npm run package:smoke, and git diff --check origin/main...HEAD. Final full diff, mergeability, one-review branch protection, and exact Roger Chappel author/committer identities re-verified.

Rebased/CI-repaired: No.

Verified head SHA: de32ce438f601c240f6c5814677b1d2a83429aa0.