Dissolve roadmap_spawn_request git rev-parse shell into git.Core.HeadCommit op (fixes medium_structure fleet-red, §3/§5)

dsl/extdeps/git/git.dag

@@ -77,6 +77,20 @@ service git.Core {
     }
   }
 
+  operation HeadCommit {
+    input {}
+    output {
+      sha: CommitSha from "stdout"
+      success: Bool from "exit_success"
+    }
+    readonly
+    transport shell { argv: ["git", "rev-parse", "HEAD"] }
+    exit {
+      0 => Unit
+      128 => String "Not a git repository"
+    }
+  }
+
   operation RemoteBranches {
     input {}
     output { branches: List<String> from "stdout_lines" }

dsl/gunbc/tools/roadmap_spawn_request.dag

@@ -1,13 +1,13 @@
 module gunbc.tools.roadmap_spawn_request
 
-import extdeps.shell
+import extdeps.git
 import gunbc.roadmap_spawner { roadmap_spawn_request_json }
 import gunbc.roadmap_authority { roadmap_authority, authored_merged_prs }
 
 func roadmap_next_spawnable() -> String {
-  let sha_result = shell.Exec.Run(script: "git rev-parse HEAD 2>/dev/null | tr -d '\\n'")
+  let sha_result = git.Core.HeadCommit()
   if sha_result.success {
-    roadmap_spawn_request_json(doc: roadmap_authority(), merged: authored_merged_prs(), anchor_commit: sha_result.stdout)
+    roadmap_spawn_request_json(doc: roadmap_authority(), merged: authored_merged_prs(), anchor_commit: sha_result.sha)
   } else {
     "{\"schema\": \"roadmap-spawn-request/v1\", \"error\": \"anchor_commit unavailable: git rev-parse HEAD failed\", \"ready\": []}"
   }

src/v2/lens/medium_structure_containment.dag

@@ -137,7 +137,6 @@ data medium_structure_exception_roster: List<String> = [
   "dsl/tools/emit_host_transport.dag",
   "dsl/gunbc/assimilate/bmc_token_federation.dag",
   "dsl/gunbc/tools/review.dag",
-  "dsl/gunbc/tools/roadmap_spawn_request.dag",
   "dsl/test/claim/fleet_converge_emit_test.dag",
 
   "dsl/test/claim/srv3_os_install_emit_test.dag",