[Error] [GitHub.copilot-chat] unhandlederror-fetch failed

[vs-code-engineering]

Error Message

unhandlederror-fetch failed

Stack Trace

TypeError: fetch failed 	at node:<REDACTED: user-file-path>:14902:13 	at process.processTicksAndRejections (node:<REDACTED: user-file-path>:103:5) 	at async t._fetch (<REDACTED: user-file-path>/.vscode-server/extensions/github.copilot-chat-0.45.1/dist/extension.js:5307:5229) 	at async t.fetch (<REDACTED: user-file-path>/.vscode-server/extensions/github.copilot-chat-0.45.1/dist/extension.js:5307:4541) 	at async gGr (<REDACTED: user-file-path>/.vscode-server/extensions/github.copilot-chat-0.45.1/dist/extension.js:5307:9266) 	at async $P.fetch (<REDACTED: user-file-path>/.vscode-server/extensions/github.copilot-chat-0.45.1/dist/extension.js:5307:13462) 	at async Kne.fetchKnownModelList (<REDACTED: user-file-path>/.vscode-server/extensions/github.copilot-chat-0.45.1/dist/extension.js:1695:18639) 	at async Kne._authChange (<REDACTED: user-file-path>/.vscode-server/extensions/github.copilot-chat-0.45.1/dist/extension.js:1695:17553)

Details

Property	Value
Bucket ID	433114d4-27a0-6681-a452-9b468129916c
Extension Version	0.45.1
Last Seen	Sun Apr 26 2026 23:57:13 GMT+0000 (Coordinated Universal Time)
Platforms	linux, darwin, win32
Product	VSCode

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This issue was automatically created from the VS Code Errors Dashboard

[vs-code-engineering]

Stable Release Anomaly Details

• Anomaly type: new (not present in 0.45.0)
• Previous stable: 0.45.0
• Current stable: 0.45.1

Related Buckets (v0.45.1)

Bucket	Users	Error Message
433114d4	24,230	fetch failed
0d3c64cc	15,831	fetch failed
6d20df53	3,618	fetch failed
63751d41	2,620	fetch failed
19d35e54	2,306	fetch failed

Combined users: ~48,605

Deminified callstack (from 433114d4):

(anonymous) (../src/extension/byok/node/byokContribution.ts:82:35)
(anonymous) (../src/extension/chat/common/fetcher.ts:34:19)
(anonymous) (../src/extension/chat/common/fetcher.ts:34:19)
(anonymous) (../src/extension/chat/common/fetcher.ts:34:19)
(anonymous) (../src/extension/chat/common/fetcher.ts:34:19)
(anonymous) (../src/extension/chat/common/fetcher.ts:89:37)

The error occurs in byokContribution.ts:82 (fetchKnownModelList) — the extension fetches a known model list and the network request fails. Multiple buckets share the same call path through the fetcher chain, differing only in platform.

Generated by errors-stable-scan · ● 10.1M · ◷

[vs-code-engineering]

🔍 Error Investigation

Summary

This is a network-level error in the GitHub.copilot-chat extension (not VS Code core). The TypeError: fetch failed occurs when the BYOK (Bring Your Own Key) contribution attempts to fetch a list of known models after an authentication change, and the underlying HTTP request fails due to network issues (DNS failure, connection timeout, proxy errors, TLS errors, etc.). The error is not a regression introduced by a specific code change — it exists across all recent extension versions (0.38.0 through 0.45.1) with 408K total hits affecting 156K users.

Culprit Commit

No VS Code core culprit commit was identified. This error originates entirely within the GitHub.copilot-chat extension code. No commit range was provided in the issue body or comments, and the error is present across at least 11 different extension versions (0.38.0–0.45.1), indicating it is a long-standing issue rather than a single-commit regression.

The recent-regression / stable-anomaly labels likely reflect a spike in extension version 0.45.1 (41K hits, 24K users since April 18) rather than a newly introduced bug.

Code Flow

The deminified stack trace reveals the following call chain within the extension:

sequenceDiagram
    participant Auth as Auth Change Event
    participant BYOK as byokContribution.ts
    participant Fetcher as fetcherServiceImpl.ts
    participant Fallback as fetcherFallback.ts
    participant Base as baseFetchFetcher.ts
    participant Node as Node.js fetch

    Auth->>BYOK: _authChange() [:63]
    BYOK->>BYOK: fetchKnownModelList() [:82]
    BYOK->>Fetcher: fetch() [:142]
    Fetcher->>Fallback: fetch with fallback [:96]
    Fallback->>Base: fetch() [:55]
    Base->>Base: _fetch() [:93]
    Base->>Node: native fetch()
    Note over Node: 💥 TypeError: fetch failed<br/>(DNS/connection/TLS failure)
    Node-->>BYOK: Unhandled rejection propagates

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Affected Files

File	Role
src/extension/byok/vscode-node/byokContribution.ts	Root cause — _authChange() at line 63 and fetchKnownModelList() at line 82 do not handle network errors gracefully
src/platform/networking/vscode-node/fetcherServiceImpl.ts	Data flow — fetch service wrapper at line 142
src/platform/networking/node/fetcherFallback.ts	Data flow — fallback fetch mechanism at line 96
src/platform/networking/node/baseFetchFetcher.ts	Crash site — _fetch() at line 93 and fetch() at line 55 where the native fetch() throws

All files are in the GitHub.copilot-chat extension source, not in VS Code core.

Repro Steps

1. Use VS Code with the GitHub.copilot-chat extension installed (any version 0.38.0+)
2. Be in an environment with unreliable network (e.g., behind a corporate proxy, VPN, restrictive firewall, or intermittent connectivity)
3. Trigger an authentication change (sign in/out of GitHub, token refresh)
4. The extension calls fetchKnownModelList() which makes an HTTP request
5. If the request fails at the network level (DNS timeout, connection refused, TLS error), the TypeError: fetch failed is thrown unhandled

This error is non-deterministic and depends on network conditions at the time of the auth change event.

Fix Proposal

The fix should be in the GitHub.copilot-chat extension, not VS Code core.

Fix location: src/extension/byok/vscode-node/byokContribution.ts → _authChange() and/or fetchKnownModelList()

Approach: Add try/catch error handling around the fetchKnownModelList() call in _authChange(). Network failures when fetching the model list should be caught and handled gracefully (e.g., log a warning, use a cached model list, or retry with backoff) rather than propagating as unhandled errors. A TypeError: fetch failed is an expected transient failure in network operations and should never surface as an unhandled error.

Recommended Owner

@bryanchen-d — default triage owner (this is a GitHub.copilot-chat extension issue; the fix is outside VS Code core and should be routed to the Copilot Chat extension team)

Generated by errors-investigate · ● 2.6M · ◷

[bryanchen-d]

@lszomoru , this seems an user error, can we catch and log it to reduce the noise of unhandled errors in telemetry?

[lszomoru]

@bryanchen-d, I do not own the fetcher code so I cannot answer this question. maybe @chrmarti?