Drop docker_cmd for graymatter; rely on JAM_FUZZ_* env vars

[tomusdrw]

Summary

• Graymatter target fails when started with the legacy `fuzz-m1-target --stay-open --listen {TARGET_SOCK}` args, so launch it with no cmd args and let it pick up `JAM_FUZZ`, `JAM_FUZZ_SOCK_PATH`, etc. from the standard target packaging env vars added in Pass standard target packaging env vars to targets #33.
• Make `docker_cmd` optional (default `""`) in `demo-source.yml`; `tests/common.ts` no longer requires `TARGET_CMD` (`buildCmdArgs("")` already collapses to no args).
• Other targets are unchanged for now — only graymatter is migrated in this PR.

Test plan

• Trigger `Fuzz: graymatter` via workflow_dispatch and confirm the demo job starts the target, the socket appears, and fuzz-m1-source completes.
• Trigger one untouched fuzz workflow (e.g. `Fuzz: jampy`) to confirm `docker_cmd`-using callers still work after the input was made optional.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Chores
  • Made docker command configuration optional in workflows and tests, allowing targets to read socket path from environment variables when no explicit command is provided.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between d235527 and fa88c8e.

📒 Files selected for processing (3)

• .github/workflows/demo-source.yml
• .github/workflows/graymatter-fuzz.yml
• tests/common.ts

💤 Files with no reviewable changes (1)

• .github/workflows/graymatter-fuzz.yml

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📝 Walkthrough

Walkthrough

The changes make the target command optional across workflow and test configuration. The docker_cmd workflow input is now optional with a default empty string, one workflow stops passing this input, and test validation no longer requires the TARGET_CMD environment variable.

Changes

Optional Target Command Configuration

Layer / File(s)	Summary
Workflow Input Definition .github/workflows/demo-source.yml	docker_cmd input changed from required to optional with empty string default; description expanded to note env-var fallback behavior.
Workflow Usage .github/workflows/graymatter-fuzz.yml	Removed docker_cmd parameter from the demo job's with: block, allowing the input to default.
Test Configuration tests/common.ts	getTargetConfig() validation now requires only TARGET_NAME and TARGET_IMAGE; TARGET_CMD is read as TARGET_CMD || "" with no error if missing.

Possibly Related PRs

• FluffyLabs/jam-testing#9: Both PRs modify how fuzz workflows and test helpers handle the target command, with this PR making docker_cmd/TARGET_CMD optional building on earlier workflow setup.
• FluffyLabs/jam-testing#28: Both PRs modify the same docker_cmd workflow input and its invocations across workflows.
• FluffyLabs/jam-testing#17: Both PRs touch the same docker_cmd workflow input in graymatter-fuzz and related workflows with inverse operations.

Poem

🐰 A command now optional, defaults to the air,
Workflows grow more flexible, with less to declare,
Tests accept the silence, when nothing is passed—
Freedom from requirements, at long last! ✨

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🎯 2 (Simple) | ⏱️ ~12 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and clearly summarizes the main change: making docker_cmd optional and allowing Graymatter to rely on environment variables instead of command-line arguments.
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.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch graymatter-no-cmd

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