Refactor Docker -e passthrough handling into shared envutil walker

[Copilot]

Semantic clustering flagged duplicated Docker -e VAR passthrough scanning in launcher and envutil. This change consolidates that traversal into one helper so expansion and logging stay aligned as Docker env-arg handling evolves.

• Shared env-arg traversal

  • Added envutil.WalkDockerEnvArgs(args, fn) to centralize detection of Docker passthrough args in the form -e VAR.
  • The helper only visits passthrough entries; explicit assignments like -e VAR=value and incomplete trailing -e flags are ignored by construction.

• ExpandEnvArgs now delegates

  • Reworked internal/envutil/expand_env_args.go to use the shared walker when building expanded -e VAR=value pairs.
  • Keeps existing behavior for unset vars and explicit VAR=value args while removing the duplicated loop skeleton.

• Launcher logging now delegates

  • Reworked internal/launcher/log_helpers.go to use the same walker for passthrough logging.
  • Preserves sanitized logging for present values and distinguishes empty-but-present variables from missing ones.

• Focused coverage

  • Added walker-specific tests covering set, empty, missing, explicit-assignment, and trailing-flag cases.
  • Updated launcher log helper coverage for empty passthrough values.

• Docs

  • Updated AGENTS.md to reflect that internal/envutil/ now owns Docker env-arg helper behavior in addition to general env utilities.

// envutil
func WalkDockerEnvArgs(args []string, fn func(index int, varName, value string, found bool))

// launcher
envutil.WalkDockerEnvArgs(args, func(_ int, varName, value string, found bool) {
    if !found {
        log.Printf("[LAUNCHER] ✗ WARNING: Env passthrough for %s requested but NOT FOUND in MCPG process", varName)
        return
    }
    if value != "" {
        log.Printf("[LAUNCHER] ✓ Env passthrough: %s=%s (from MCPG process)", varName, sanitize.TruncateSecret(value))
        return
    }
    log.Printf("[LAUNCHER] ⚠️  Env passthrough for %s is empty in MCPG process", varName)
})

[Copilot]

Pull request overview

This PR consolidates Docker -e VAR passthrough argument detection into a single helper in internal/envutil, then reuses it to keep environment expansion behavior and launcher passthrough logging consistent as the Docker arg handling evolves.

Changes:

• Added envutil.WalkDockerEnvArgs to centralize traversal of Docker passthrough env args (-e VAR, excluding -e VAR=value and trailing -e).
• Refactored envutil.ExpandEnvArgs to delegate passthrough detection to the shared walker.
• Refactored launcher passthrough logging to use the shared walker and added coverage for empty-but-present env vars.

Show a summary per file

File	Description
internal/launcher/log_helpers.go	Replaces bespoke -e scanning with envutil.WalkDockerEnvArgs and logs empty-but-present vars distinctly.
internal/launcher/log_helpers_test.go	Adds a test to cover logging behavior when a passthrough variable is present but empty.
internal/envutil/expand_env_args.go	Introduces WalkDockerEnvArgs and refactors ExpandEnvArgs to reuse it.
internal/envutil/expand_env_args_test.go	Adds walker-focused tests for set/empty/missing vars and ignores explicit assignments/trailing -e.
AGENTS.md	Updates project structure note to reflect Docker env-arg utilities living in internal/envutil/.

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• Files reviewed: 5/5 changed files
• Comments generated: 1