refactor: replace hardcoded /opt/gh-aw paths with GH_AW_HOME constants (partial)

[Copilot]

Hardcoded /opt/gh-aw paths throughout the compiler prevent self-hosted runners from relocating the installation directory. This PR introduces typed constants and a helper to abstract all path references, allowing operators to override via GH_AW_HOME.

New abstractions (pkg/workflow/setup_action_paths.go)

Constant/Helper	Value	Use in
GhAwHome	${GH_AW_HOME}	bash run: blocks
GhAwHomeJS	process.env.GH_AW_HOME	JS require() expressions
GhAwHomeExpr	${{ env.GH_AW_HOME }}	YAML env: blocks
GhAwHomeExprDefault	${{ env.GH_AW_HOME || '/opt/gh-aw' }}	job-level env with fallback
JsRequireGhAw(path)	helper	generates process.env.GH_AW_HOME + '/path'

SetupActionDestination updated to GhAwHomeExpr + "/actions".

pkg/constants/constants.go

• Added GhAwHomeDefault = "/opt/gh-aw"
• Updated DefaultGhAwMount to \${GH_AW_HOME}:\${GH_AW_HOME}:ro (shell-expanded at runtime)

Example replacement pattern

// Before
yaml.WriteString("const { main } = require('/opt/gh-aw/actions/redact_secrets.cjs');\n")
yaml.WriteString("bash /opt/gh-aw/actions/stop_mcp_gateway.sh\n")

// After
yaml.WriteString("const { main } = require(" + JsRequireGhAw("actions/redact_secrets.cjs") + ");\n")
yaml.WriteString("bash " + GhAwHome + "/actions/stop_mcp_gateway.sh\n")

Status

~20 compiler files updated. Remaining: notify_comment.go, compiler_main_job.go (GH_AW_HOME job-level env injection), compiler_yaml.go, cache.go, safe_jobs.go, maintenance_workflow.go, mcp_github_config.go, several others, JS .cjs files, test updates, and lock file recompilation.

[pelikhan]

@copilot keep working

[github-actions]

Hey @Copilot 👋 — great start on the GH_AW_HOME path-abstraction refactor! Centralizing the hardcoded /opt/gh-aw paths behind typed constants (GhAwHome, GhAwHomeJS, GhAwHomeExprDefault, and the JsRequireGhAw helper) is exactly the kind of change that makes self-hosted runner deployments much more flexible. The description table and before/after examples are excellent.

A couple of things to close out before this can leave draft:

• No tests yet — the PR body already flags "test updates" as a remaining item, and the checklist confirms no _test.go files were touched. The codebase has good coverage patterns to follow: pkg/workflow/cjs_require_validation_test.go already tests .cjs require paths, and pkg/workflow/agentic_workflow_test.go / pkg/workflow/agentic_output_test.go exercise many of the compiled YAML paths that now reference the new constants. Any test that asserts a generated YAML snippet containing /opt/gh-aw should be updated to expect the $\{\{ env.GH_AW_HOME || '/opt/gh-aw' }} (or shell-variable) form.

• Remaining files — notify_comment.go, compiler_main_job.go, compiler_yaml.go, cache.go, safe_jobs.go, maintenance_workflow.go, mcp_github_config.go, and the JS .cjs files are still pending per the status section. The PR should be complete (or explicitly scoped with a follow-up issue) before merging.

• Run make agent-finish — once the remaining files and tests are in place, run make agent-finish (build + test + lint + recompile + fmt) to confirm everything is green, as required by the contribution process.

If you'd like a hand finishing up, you can assign this prompt to your coding agent:

Continue the GH_AW_HOME path-abstraction refactor in the gh-aw repository on branch copilot/reimplement-gh-aw-home-support.

Context:
- pkg/workflow/setup_action_paths.go already defines GhAwHome, GhAwHomeJS, GhAwHomeExpr, GhAwHomeExprDefault, and JsRequireGhAw().
- pkg/constants/constants.go now has GhAwHomeDefault = "/opt/gh-aw" and an updated DefaultGhAwMount.
- ~20 compiler files have already been migrated.

Tasks:
1. Migrate the remaining files that still contain hardcoded /opt/gh-aw paths:
   - pkg/workflow/notify_comment.go
   - pkg/workflow/compiler_main_job.go  (also inject GH_AW_HOME job-level env)
   - pkg/workflow/compiler_yaml.go
   - pkg/workflow/cache.go
   - pkg/workflow/safe_jobs.go
   - pkg/workflow/maintenance_workflow.go
   - pkg/workflow/mcp_github_config.go
   - Any remaining .go files: run `grep -r '/opt/gh-aw' pkg/` to find stragglers.
   - JS .cjs files under actions/ that hardcode /opt/gh-aw.

2. Update tests:
   - In pkg/workflow/cjs_require_validation_test.go, pkg/workflow/agentic_workflow_test.go, and any other test that asserts YAML output containing /opt/gh-aw literals, update expected strings to use the new constant forms (e.g. process.env.GH_AW_HOME, \$\{GH_AW_HOME}, $\{\{ env.GH_AW_HOME || '/opt/gh-aw' }}).
   - Add a unit test in pkg/workflow/ that calls JsRequireGhAw("actions/redact_secrets.cjs") and asserts the returned string equals `process.env.GH_AW_HOME + '/actions/redact_secrets.cjs'`.

3. Run `make agent-finish` to validate the full build, test, lint, recompile, and format pipeline passes before committing.

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[pelikhan]

see #21443