ci: RTL testbenches and zero-multiplier check in CI (M4 Task 7 step 2)

[jackthepunished]

Per docs/plans/2026-08-07-phase4-m4-rtl.md Task 7 step 2: CI now installs verilator+yosys and runs make lint rtl_test synth_check after the existing make test. rtl_test includes the export64 case (needs the cpu torch already installed for pytest); nothing depends on data/v1. Expect the job to lengthen by roughly the synth_xilinx runtime. Merging only after this PR's own workflow run is green.

Summary by CodeRabbit

• Chores
  • Enhanced automated validation by installing additional hardware design tools.
  • Added linting, RTL tests, and synthesis checks to the continuous integration workflow.

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[coderabbitai]

📝 Walkthrough

Walkthrough

The CI test job now installs Verilator and Yosys. It runs linting, RTL tests, and synthesis checks after the existing Python test suite.

Changes

CI validation

Layer / File(s)	Summary
RTL checks in CI .github/workflows/ci.yml	The test job installs Verilator and Yosys. It runs make lint rtl_test and make synth_check after the Python tests.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the CI changes, including RTL tests and the zero-multiplier synthesis check.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch m4-ci

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In @.github/workflows/ci.yml:
- Line 15: Update the Makefile:synth_check recipe invoked by the CI run to
ensure Yosys failures propagate through its tee pipeline, either by enabling
pipefail for the recipe shell or by removing the pipeline; keep synth_check
failing whenever Yosys fails.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: ab563f6c-b898-48ca-9456-d60de3ce9c08

📥 Commits

Reviewing files that changed from the base of the PR and between 0cfc32b and 4b0b387.

📒 Files selected for processing (1)

• .github/workflows/ci.yml

[coderabbitai]

🎯 Functional Correctness | 🟠 Major | ⚡ Quick win

Make synth_check propagate Yosys failures.

Line 15 relies on Makefile:synth_check, which runs Yosys through tee without enabling pipefail. In shells without pipefail, the pipeline status is the last command’s status, so a successful tee can hide a failed Yosys process. (pubs.opengroup.org)

Update synth_check to use a shell with pipefail, or avoid the pipeline, before relying on this step as a synthesis gate.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In @.github/workflows/ci.yml at line 15, Update the Makefile:synth_check recipe
invoked by the CI run to ensure Yosys failures propagate through its tee
pipeline, either by enabling pipefail for the recipe shell or by removing the
pipeline; keep synth_check failing whenever Yosys fails.