agentHost: auto-approve reads of Copilot SDK tool-output temp files

[roblourens]

What

When a tool result is too large to fit inline, the Copilot SDK spills it to a temp file under os.tmpdir() (named like copilot-tool-output-<…>.txt or <ts>-copilot-tool-output-<…>.txt) and then asks the model to read that file back in a follow-up turn. Today the agent host prompts the user for permission on every one of those reads, even though the file was just written by the SDK on our behalf.

This change auto-approves those read permission requests, mirroring the existing session-state auto-approval pattern in CopilotAgentSession.

How

• New helper isCopilotSdkToolOutputTempFile(filePath, tmpDir) in copilotAgentSession.ts:
  • Requires the file's parent directory to be exactly os.tmpdir() (no nested subdirs)
  • Requires the basename to match one of the two SDK naming layouts:
    • <timestamp>-copilot-tool-output-<6-char-id>.txt
    • copilot-tool-output-<timestamp>-<6-char-id>.txt
• In handlePermissionRequest, after the existing session-state branch, auto-approve when request.kind === 'read' and the path matches the helper.
• Intentionally read-only — writes to these paths still confirm.

How to repro the original prompt

Ask the agent something like:

Run find /usr -type f and then tell me how many of the results contain "lib". Don't summarize — actually look at the full output.

The shell tool result spills to os.tmpdir()/…copilot-tool-output-….txt, and the follow-up read of that file is what was prompting before this change.

Tests

Added 4 unit tests in copilotAgentSession.test.ts covering:

• positive case for both SDK filename layouts
• tool-output-named files outside tmpDir are not auto-approved
• unrelated files inside tmpDir are not auto-approved
• write to a tool-output path is not auto-approved

All 78 tests in the suite pass; compile-check-ts-native is clean.

Notes for reviewers

• The EH CLI (extensions/copilot/src/extension/chatSessions/copilotcli/node/permissionHelpers.ts) does not currently have parity for this. Out of scope for this PR — happy to follow up.

(Written by Copilot)

[Copilot]

Pull request overview

This PR reduces permission prompts in the agent host by auto-approving read permission requests for Copilot SDK “spilled” large tool outputs stored as temp files under os.tmpdir(), aligning with the existing auto-approval behavior for internal session-state files.

Changes:

• Add temp-file pattern detection (isCopilotSdkToolOutputTempFile) for Copilot SDK tool-output spill files.
• Auto-approve read permission requests when the requested path matches the Copilot SDK temp-file pattern in tmpDir.
• Add unit tests covering positive/negative cases and ensuring write is not auto-approved.

Show a summary per file

File	Description
src/vs/platform/agentHost/node/copilot/copilotAgentSession.ts	Adds temp-file detection + auto-approval path for read permission requests targeting Copilot SDK spill files in the OS temp directory.
src/vs/platform/agentHost/test/node/copilotAgentSession.test.ts	Adds tests for the new auto-approval behavior and its expected boundaries.

Copilot's findings

Comments suppressed due to low confidence (1)

src/vs/platform/agentHost/node/copilot/copilotAgentSession.ts:627

• Auto-approving reads in the global OS temp directory based only on basename pattern can leak unrelated local data: any pre-existing file (or symlink) in tmpDir with a matching name would be read without user confirmation. Consider tightening this by validating the target is an actual regular file (not a symlink) and narrowing the match (e.g., enforce expected timestamp/id lengths), or preferably auto-approve only paths that were observed/recorded as SDK-created spill files for this session.

			// Auto-approve reads of large-tool-output temp files written by the
			// Copilot SDK itself. The SDK spills oversized tool results to
			// `os.tmpdir()/copilot-tool-output-…txt` and then asks the model
			// to read them back in a follow-up turn — no need to confirm.
			if (request.kind === 'read' && typeof request.path === 'string') {
				if (isCopilotSdkToolOutputTempFile(request.path, this._environmentService.tmpDir.fsPath)) {
					this._logService.info(`[Copilot:${this.sessionId}] Auto-approving Copilot SDK tool-output temp file ${request.path}`);
					return { kind: 'approve-once' };
				}
			}

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