fix(evidence): bind corpus to workspace identity

harness/tht/corpus/pipeline.py

@@ -85,6 +85,16 @@ class CorpusPipeline:
         self.retain_published_generations = retain_published_generations
         self.workspace_id = workspace_id
 
+    def _assert_workspace_binding(self) -> None:
+        manifest = self.store.active_manifest()
+        if manifest is None:
+            return
+        persisted = manifest.metadata.get("workspace_id")
+        if persisted != self.workspace_id:
+            raise PipelineError(
+                "corpus belongs to a different workspace; use a new corpus root or explicit rebuild"
+            )
+
     def _protected_generations(self, workspace_root: Path) -> set[str]:
         protected = {value for value in (self.store.active_generation(),) if value}
         runs = workspace_root / ".tht-jobs" / "evidence" / "runs"
@@ -102,11 +112,7 @@ class CorpusPipeline:
         return protected
 
     def gc(self, *, workspace_root: Path, dry_run: bool = False) -> dict:
-        active_manifest = self.store.active_manifest()
-        if active_manifest is not None:
-            persisted_workspace = active_manifest.metadata.get("workspace_id")
-            if isinstance(persisted_workspace, str):
-                self.workspace_id = persisted_workspace
+        self._assert_workspace_binding()
         published = self.store.published_generations()
         list_vectors = getattr(self.vector_store, "list_evidence_generations", None)
         vector_generations = set(list_vectors("evidence", self.workspace_id)) if list_vectors else set()
@@ -166,11 +172,13 @@ class CorpusPipeline:
 
     def run(self, *, dry_run: bool = False, resume: str | None = None) -> PipelineResult:
         with self.store.writer_lock():
+            self._assert_workspace_binding()
             return self._run(dry_run=dry_run, resume=resume)
 
     def run_as_job(self, **kwargs) -> PipelineResult:
         self.workspace_id = kwargs["workspace_id"]
         with self.store.writer_lock():
+            self._assert_workspace_binding()
             return self._run_as_job(**kwargs)
 
     def _run_as_job(