fix(#2516): resolve executor_model inherit literal passthrough; add regression test (#2537)

When model_profile is "inherit", execute-phase was passing the literal string
"inherit" to Task(model=), causing fallback to the default model. The workflow
now documents that executor_model=="inherit" requires omitting the model= parameter
entirely so Claude Code inherits the orchestrator model automatically.

Closes #2516

get-shit-done/workflows/execute-phase.md

@@ -74,6 +74,8 @@ AGENT_SKILLS=$(gsd-sdk query agent-skills gsd-executor 2>/dev/null)
 
 Parse JSON for: `executor_model`, `verifier_model`, `commit_docs`, `parallelization`, `branching_strategy`, `branch_name`, `phase_found`, `phase_dir`, `phase_number`, `phase_name`, `phase_slug`, `plans`, `incomplete_plans`, `plan_count`, `incomplete_count`, `state_exists`, `roadmap_exists`, `phase_req_ids`, `response_language`.
 
+**Model resolution:** If `executor_model` is `"inherit"`, omit the `model=` parameter from all `Task()` calls — do NOT pass `model="inherit"` to Task. Omitting the `model=` parameter causes Claude Code to inherit the current orchestrator model automatically. Only set `model=` when `executor_model` is an explicit model name (e.g., `"claude-sonnet-4-6"`, `"claude-opus-4-7"`).
+
 **If `response_language` is set:** Include `response_language: {value}` in all spawned subagent prompts so any user-facing output stays in the configured language.
 
 Read worktree config:
@@ -421,7 +423,10 @@ Execute each selected wave in sequence. Within a wave: parallel if `PARALLELIZAT
    Task(
      subagent_type="gsd-executor",
      description="Execute plan {plan_number} of phase {phase_number}",
-     model="{executor_model}",
+     # Only include model= when executor_model is an explicit model name.
+     # When executor_model is "inherit", omit this parameter entirely so
+     # Claude Code inherits the orchestrator model automatically.
+     model="{executor_model}",  # omit this line when executor_model == "inherit"
      isolation="worktree",
      prompt="
        <objective>