fix(core): derive workspace session store from the engine store path (#1926)

getOrCreateWorkspaceAgent built the per-workspace session file as
filepath.Join(filepath.Dir(e.sessions.StorePath()), ...). With no store
path configured — which is how every engine in the test suite is built —
filepath.Dir("") is ".", so the path collapsed to a bare relative
"<engine>_ws_<hash>.json" and the session manager wrote it into the
process working directory. That is what littered core/ with test_ws_*.json
during `go test ./core/`.

An empty store path already means "no persistence" everywhere else in the
session manager (saveLocked returns early), so it now means the same here:
the workspace manager is built unpersisted instead of inventing a path.
A configured store path still derives the workspace file beside it, as
before.

Regressions: an engine without a store path yields a workspace manager
whose StorePath() is empty, and a configured one still derives
test_ws_<hash>.json in the store's directory.

Also ignores the stale files contributors already have on disk.

Co-authored-by: Claude Code <noreply@anthropic.com>

.gitignore

@@ -82,6 +82,13 @@ temp/
 *.pid
 *.log
 
+# Per-workspace session stores (<engine>_ws_<hash>.json, see
+# Engine.getOrCreateWorkspaceAgent). They are derived from the engine's own
+# session store, so they belong next to it — never in the working tree. This
+# is a guard for files already on disk from before that derivation was
+# corrected; the derivation itself no longer produces them.
+*_ws_????????.json
+
 # ============================================================================
 # IDE & Editor
 # ============================================================================

core/engine.go

@@ -4180,10 +4180,17 @@ func (e *Engine) getOrCreateWorkspaceAgent(workspace string) (Agent, *SessionMan
 		}
 	}
 
-	// Create per-workspace session manager
+	// Create per-workspace session manager. An empty store path means "no
+	// persistence" everywhere else in the session manager, so it has to mean
+	// the same here: filepath.Dir("") is ".", which would otherwise drop
+	// "<engine>_ws_<hash>.json" into the process working directory — that is
+	// what littered core/ with test_ws_*.json during `go test ./core/`.
 	h := sha256.Sum256([]byte(workspace))
-	sessionFile := filepath.Join(filepath.Dir(e.sessions.StorePath()),
-		fmt.Sprintf("%s_ws_%s.json", e.name, hex.EncodeToString(h[:4])))
+	sessionFile := ""
+	if storePath := e.sessions.StorePath(); storePath != "" {
+		sessionFile = filepath.Join(filepath.Dir(storePath),
+			fmt.Sprintf("%s_ws_%s.json", e.name, hex.EncodeToString(h[:4])))
+	}
 	sessions := NewSessionManager(sessionFile)
 	sessions.InvalidateForAgent(agent.Name())
 

core/workspace_session_store_test.go

@@ -0,0 +1,66 @@
+package core
+
+import (
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+// registerWorkspaceStoreAgent registers a throwaway agent type so
+// getOrCreateWorkspaceAgent can build a per-workspace instance.
+func registerWorkspaceStoreAgent(t *testing.T, agentName string) {
+	t.Helper()
+	RegisterAgent(agentName, func(opts map[string]any) (Agent, error) {
+		workDir, _ := opts["work_dir"].(string)
+		return &sendWorkDirAgent{
+			name:    agentName,
+			workDir: workDir,
+			session: newResultAgentSession("workspace session"),
+		}, nil
+	})
+}
+
+// A workspace session manager has to inherit the engine's "no store path means
+// no persistence" contract. filepath.Dir("") is ".", so deriving a path from an
+// empty store path used to drop "<engine>_ws_<hash>.json" into the process
+// working directory — that is how `go test ./core/` littered core/ with
+// test_ws_*.json files.
+func TestGetOrCreateWorkspaceAgent_EmptyStorePathStaysUnpersisted(t *testing.T) {
+	agentName := "test-ws-store-unpersisted"
+	registerWorkspaceStoreAgent(t, agentName)
+
+	p := &stubPlatformEngine{n: "telegram"}
+	e := NewEngine("test", &sendWorkDirAgent{name: agentName}, []Platform{p}, "", LangEnglish)
+
+	_, sessions, err := e.getOrCreateWorkspaceAgent(t.TempDir())
+	if err != nil {
+		t.Fatalf("getOrCreateWorkspaceAgent() error = %v", err)
+	}
+	if got := sessions.StorePath(); got != "" {
+		t.Fatalf("workspace store path = %q, want empty when the engine has no store path", got)
+	}
+}
+
+// The derived path keeps living beside the engine's own store, so a configured
+// deployment still persists workspace sessions.
+func TestGetOrCreateWorkspaceAgent_DerivesStorePathBesideEngineStore(t *testing.T) {
+	agentName := "test-ws-store-derived"
+	registerWorkspaceStoreAgent(t, agentName)
+
+	dir := t.TempDir()
+	p := &stubPlatformEngine{n: "telegram"}
+	e := NewEngine("test", &sendWorkDirAgent{name: agentName}, []Platform{p},
+		filepath.Join(dir, "sessions.json"), LangEnglish)
+
+	_, sessions, err := e.getOrCreateWorkspaceAgent(t.TempDir())
+	if err != nil {
+		t.Fatalf("getOrCreateWorkspaceAgent() error = %v", err)
+	}
+	got := sessions.StorePath()
+	if filepath.Dir(got) != dir {
+		t.Fatalf("workspace store dir = %q, want %q", filepath.Dir(got), dir)
+	}
+	if base := filepath.Base(got); !strings.HasPrefix(base, "test_ws_") || !strings.HasSuffix(base, ".json") {
+		t.Fatalf("workspace store name = %q, want test_ws_<hash>.json", base)
+	}
+}