Empty sessions view: cannot call joinPath

[aeschli]

FIY @sandy081 @bpasero Maybe you want to revisit unknown:///, not clear what kind of errors the user will see with this unresolvable location.

[vs-code-engineering]

📬 CODENOTIFY

The following users are being notified based on files changed in this PR:

@jrieken

Matched files:

• src/vs/base/common/uri.ts

[github-actions]

Screenshot Changes

Base: b8258174 Current: 8933fb8a

Changed (3)

chat/aiCustomizations/aiCustomizationManagementEditor/McpBrowseMode/Light

Before	After

editor/inlineCompletions/other/JumpToHint/Dark

Before	After

agentSessionsViewer/NeedsInput/Dark

Before	After

[Copilot]

Pull request overview

Fixes a crash in the Agents/Sessions window caused by URI.joinPath being invoked on URIs with an empty/missing path (e.g. empty sessions view / missing repo metadata), which previously threw [UriError]: cannot call joinPath on URI without path.

Changes:

• Adjusts the Copilot chat sessions adapter to use a fallback repository URI that includes a path (unknown:///) when repo metadata is missing.
• Changes URI.joinPath to treat an empty path as '/' instead of throwing.

Show a summary per file

File	Description
src/vs/sessions/contrib/copilotChatSessions/browser/copilotChatSessionsProvider.ts	Uses a safer fallback URI (unknown:///) to avoid downstream joinPath failures when repo URI is missing.
src/vs/base/common/uri.ts	Alters core URI.joinPath behavior for empty-path URIs (no longer throws; normalizes to '/').

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 1

[Copilot]

URI.joinPath used to throw for URIs without a path (e.g. URI.parse('foo:') or URI.parse('foo://bar')). With this change it will silently treat an empty path as '/', which contradicts the existing contract validated by src/vs/base/test/common/uri.test.ts (the URI#joinPath test currently asserts these cases throw) and will break those tests/consumers. Consider keeping the throw and fixing the callers that construct path-less URIs (ensure they use a '/' path), or narrowly applying the fallback only for schemes where empty-path join semantics are well-defined and tests are updated accordingly.

Suggested change

	// treat empty path as slash to simplify join and normalization
	uri = uri.with({ path: _slash });
	throw new Error(`[UriError]: cannot join path on URI without path`);