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Description
Updated to latest 0.14.0 Copilot today, Eclipse 4.38.
GitHub Copilot 0.14.0.202512112209 com.microsoft.copilot.eclipse.feature.feature.group GitHub Copilot
Chat view is unusable. Any request / prompt shows the error below, with different models in "Ask" mode on different files and with trivial questions like /explain or "what does this class?".
org.eclipse.lsp4e
Error
Fri Dec 12 09:21:45 CET 2025
[Error] [chat] Error processing turn 861097da-6faf-43c8-9c8c-2b5eb97f9848 Error: maxTokens must be larger than the ellipsis length
at t.elide (/snapshot/copilot-client/prompt/src/elidableText/elidableText.ts:118:19)
at /snapshot/copilot-client/lib/src/conversation/prompt/conversationPromptEngine.ts:112:72
at Array.map (<anonymous>)
at q0.elideChatMessages (/snapshot/copilot-client/lib/src/conversation/prompt/conversationPromptEngine.ts:105:14)
at q0.toPrompt (/snapshot/copilot-client/lib/src/conversation/prompt/conversationPromptEngine.ts:67:45)
at processTicksAndRejections (node:internal/process/task_queues:105:5)
at Zz.buildConversationPrompt (/snapshot/copilot-client/lib/src/conversation/turnProcessorStrategy.ts:79:16)
at Bje.processWithModel (/snapshot/copilot-client/lib/src/conversation/turnProcessor.ts:189:36)
at Bje.process (/snapshot/copilot-client/lib/src/conversation/turnProcessor.ts:90:13)
at handleConversationCreateChecked (/snapshot/copilot-client/agent/src/methods/conversation/conversationCreate.ts:137:5)
It looks like the problem appears because we have few (~50) projects containing .github/copilot-instructions.md files in the workspace.
If I make the file empty, the problem disappears.
Note: the Chat view was asked on a fully unrelated file from a different project, on which the instructions of other projects shouldn't apply at all.
Update
It looks like there is a max limit of characters that could be used in .github/copilot-instructions.md file, multiplied by number of files in git repository.
With ~1700 characters for ~50 projects Chat view shows an error, with ~1300 it seem to work.
Reducing number of files also helps.
So the bug is:
Copilot plugin puts all found .github/copilot-instructions.md files from all projects into the context of the conversation in a Chat view, even if conversation scope is a file in a fully unrelated project (from the same git repository).
The first project below, with no instructions at all still seem to be affected by instructions from other projects
common git repo
--> Project/<no github instructions>
--> ProjectA/.github/copilot-instructions.md
--> ProjectB/.github/copilot-instructions.md
--> ProjectC/.github/copilot-instructions.md
--> ProjectD/.github/copilot-instructions.md
--> ProjectE/.github/copilot-instructions.md
--> ProjectF/.github/copilot-instructions.md