[timothyanderson096-ocdealcheck]

Allow LocalNode write callbacks to suppress the default data-store write by returning anything except None, while still invoking all registered callbacks in order. Addresses the requested enhancement in #598, reported by @sveinse and discussed with @acolomb.

Use an explicit is not None check after each callback and return only after the loop. This implements the discussion's stated non-None/all-callback contract without truthiness or generator short-circuiting. False, 0 and empty values also opt out. Document arguments, order, return semantics and exception propagation in the callback registration API.

Compatibility change: previously ignored non-None callback return values now suppress storage. Existing callbacks needing normal storage must return None. Prior stored data is left unchanged when opting out. Validation still precedes callbacks; callback exceptions propagate and prevent storage as before. Read-callback behavior, async dispatch and registration concurrency are unchanged.

Validation recorded 25 October 2026, Linux / CPython 3.12.14 / python-can 4.6.1: six of eleven requested-contract tests fail on original production source and five controls pass; these demonstrate an unimplemented enhancement, not six existing defects. Final focused new/existing LocalNode tests 30 passed, independently rerun. Full base suite 291 passed, one optional-export skip; export-enabled 292 passed; docs build succeeds and includes the callback contract. Fresh original/final optional mypy both retain 44 identical inherited errors in seven files, exit 1.

Tests cover false/empty/truthiness-resistant results, all-callback order, prior data preservation, default copying, kwargs, pre-callback rejection, exceptions, unchanged reads, NMT side effects and real client/server SDO callback round trips without a connected CAN backend. Baseline/final test ASTs match; two formatting-only wraps do not alter assertions.

On 27 October, public head bea9b0443464c482eab6f2cf6590e95de8747daa, tree 372d057a337c52a3ad2939e7be960f3aa3337d6d, exactly matches clean tested 3dfa5b5 on unchanged base 14b3336. Saved evidence and independent review were checked; no fresh project-suite rerun during publication. Related #676 subscriber dispatch and #359 async work do not supply this LocalNode storage behavior.

Physical devices, other OS/Python/minimum dependencies, async callbacks, concurrent registration, real application migration and integration with other prepared branches remain unvalidated. This is a proposed API enhancement, not an accepted compatibility policy or upstream approval.

Prepared with AI assistance and independent inspection during original preparation.

Timothy Anderson — Spotted Ridge Engineering / OC Labs
Independent software verification · GDN (Global Decision Network)
timothyanderson096@gmail.com · Engineering evidence