From 3861a9f6e8bc2000791eff879ad773028fc1ebfb Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Tue, 19 May 2026 16:25:44 +0000
Subject: [PATCH 1/3] Initial plan


From 067a529141356b012004d32ccd00d53dbe6d1500 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Tue, 19 May 2026 16:40:45 +0000
Subject: [PATCH 2/3] Handle stale config-retained projects without panic

Co-authored-by: RyanCavanaugh <6685088+RyanCavanaugh@users.noreply.github.com>
---
 internal/project/projectcollectionbuilder.go  |  5 +-
 ...ojectcollectionbuilder_panic_repro_test.go | 70 +++++++++++++++++++
 2 files changed, 74 insertions(+), 1 deletion(-)
 create mode 100644 internal/project/projectcollectionbuilder_panic_repro_test.go

diff --git a/internal/project/projectcollectionbuilder.go b/internal/project/projectcollectionbuilder.go
index e3d3e6a4c46..e826c8207ec 100644
--- a/internal/project/projectcollectionbuilder.go
+++ b/internal/project/projectcollectionbuilder.go
@@ -612,7 +612,10 @@ func (b *ProjectCollectionBuilder) markProjectsAffectedByConfigChanges(
 	for projectPath := range configChangeResult.affectedProjects {
 		project, ok := b.configuredProjects.Load(projectPath)
 		if !ok {
-			panic(fmt.Sprintf("project %s affected by config change not found", projectPath))
+			if logger != nil {
+				logger.Logf("Skipping stale project %s affected by config change", projectPath)
+			}
+			continue
 		}
 		project.ChangeIf(
 			func(p *Project) bool { return !p.dirty || p.dirtyFilePath != "" },
diff --git a/internal/project/projectcollectionbuilder_panic_repro_test.go b/internal/project/projectcollectionbuilder_panic_repro_test.go
new file mode 100644
index 00000000000..860d657a097
--- /dev/null
+++ b/internal/project/projectcollectionbuilder_panic_repro_test.go
@@ -0,0 +1,70 @@
+package project
+
+import (
+	"context"
+	"testing"
+
+	"github.com/microsoft/typescript-go/internal/bundled"
+	"github.com/microsoft/typescript-go/internal/lsp/lsproto"
+	"github.com/microsoft/typescript-go/internal/project/logging"
+	"github.com/microsoft/typescript-go/internal/tspath"
+	"github.com/microsoft/typescript-go/internal/vfs/vfstest"
+)
+
+func TestProjectCollectionBuilder_PanicOnStaleConfigRetainer(t *testing.T) {
+	t.Parallel()
+
+	if !bundled.Embedded {
+		t.Skip("bundled files are not embedded")
+	}
+
+	files := map[string]any{
+		"/src/tsconfig.json": `{"compilerOptions": {"strict": true}}`,
+		"/src/index.ts":      `export const x = 1;`,
+	}
+
+	fs := bundled.WrapFS(vfstest.FromMap(files, false /*useCaseSensitiveFileNames*/))
+	session := NewSession(&SessionInit{
+		BackgroundCtx: context.Background(),
+		Options: &SessionOptions{
+			CurrentDirectory:   "/",
+			DefaultLibraryPath: bundled.LibPath(),
+			TypingsLocation:    "/home/src/Library/Caches/typescript",
+			PositionEncoding:   lsproto.PositionEncodingKindUTF8,
+			WatchEnabled:       false,
+			LoggingEnabled:     false,
+		},
+		FS:          fs,
+		Client:      noopClient{},
+		Logger:      logging.NewTestLogger(),
+		NpmExecutor: nil,
+	})
+
+	session.DidOpenFile(
+		context.Background(),
+		lsproto.DocumentUri("file:///src/index.ts"),
+		1,
+		files["/src/index.ts"].(string),
+		lsproto.LanguageKindTypeScript,
+	)
+
+	snapshot := session.Snapshot()
+	configPath := session.toPath("/src/tsconfig.json")
+	entry := snapshot.ConfigFileRegistry.configs[configPath]
+	if entry == nil {
+		t.Fatal("expected /src/tsconfig.json config entry to exist")
+	}
+	if entry.retainingProjects == nil {
+		entry.retainingProjects = make(map[tspath.Path]struct{})
+	}
+	entry.retainingProjects[session.toPath("/stale/tsconfig.json")] = struct{}{}
+
+	session.DidChangeWatchedFiles(context.Background(), []*lsproto.FileEvent{
+		{
+			Uri:  lsproto.DocumentUri("file:///src/tsconfig.json"),
+			Type: lsproto.FileChangeTypeChanged,
+		},
+	})
+
+	_, _ = session.GetLanguageService(context.Background(), lsproto.DocumentUri("file:///src/index.ts"))
+}

From 96b194a189ccef43da42bf0a6c675856b6c28237 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Tue, 19 May 2026 16:41:54 +0000
Subject: [PATCH 3/3] Polish stale-config repro and logging

Co-authored-by: RyanCavanaugh <6685088+RyanCavanaugh@users.noreply.github.com>
---
 internal/project/projectcollectionbuilder.go                  | 2 +-
 internal/project/projectcollectionbuilder_panic_repro_test.go | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/internal/project/projectcollectionbuilder.go b/internal/project/projectcollectionbuilder.go
index e826c8207ec..41ad6821f5f 100644
--- a/internal/project/projectcollectionbuilder.go
+++ b/internal/project/projectcollectionbuilder.go
@@ -613,7 +613,7 @@ func (b *ProjectCollectionBuilder) markProjectsAffectedByConfigChanges(
 		project, ok := b.configuredProjects.Load(projectPath)
 		if !ok {
 			if logger != nil {
-				logger.Logf("Skipping stale project %s affected by config change", projectPath)
+				logger.Logf("Skipping stale project %s affected by config change (project may have been removed)", projectPath)
 			}
 			continue
 		}
diff --git a/internal/project/projectcollectionbuilder_panic_repro_test.go b/internal/project/projectcollectionbuilder_panic_repro_test.go
index 860d657a097..52db80e745b 100644
--- a/internal/project/projectcollectionbuilder_panic_repro_test.go
+++ b/internal/project/projectcollectionbuilder_panic_repro_test.go
@@ -11,7 +11,7 @@ import (
 	"github.com/microsoft/typescript-go/internal/vfs/vfstest"
 )
 
-func TestProjectCollectionBuilder_PanicOnStaleConfigRetainer(t *testing.T) {
+func TestProjectCollectionBuilder_HandlesStaleConfigRetainer(t *testing.T) {
 	t.Parallel()
 
 	if !bundled.Embedded {