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[RefImpl] Add a GitHub Copilot CLI host adapter #114
Description
Target runtime or language
Github Copilot CLI
What this proves
I tested Copilot CLI’s hook API locally. Its session and tool hooks appear sufficient for an ACS adapter:
| ACS | Copilot CLI |
|---|---|
| Session lifecycle | sessionStart, sessionEnd |
| Tool request | preToolUse |
| Tool result | postToolUse, postToolUseFailure |
| Tool decision | permissionDecision |
| Session ID | sessionId |
| Workspace | cwd |
The adapter would mainly need to translate tool names and payloads, Guardian decisions, tool results, and audit events.
A few details still need to be handled carefully, especially tool-name mapping (bash vs. Bash), non-zero shell exits, hook timeouts, and multiple-hook behavior.
Do you intend to implement this yourself
Yes, I want this assigned to me
Current Priority Scope
This is deferred or out of scope and I am filing it to be tracked
Activity
Lrd0036 commentedon Oct 13, 2026
@DvJiang thank you for testing... are you still planning on taking this slice? If so, I'd like to help: the Codex adapter in #162 and I went through Copilot's hooks reference. If you've moved on, I'm happy to take it. Either way, here's what I found:
preToolUsereturnspermissionDecisionplusmodifiedArgs, which covers ACS MODIFY.postToolUsecan returnmodifiedResult, so a result gate can replace what the model sees? The CC host's hookmap was built so a second host is "a shim and a hookmap rather than a fork," and Copilot fitsreference-implementations/agt/hosts/. One difference:toolArgsarrives as a JSON string, so it needs a parse step.Needs a decision:
timeoutSec(default 30) is treated as allowed. github/copilot-cli#2893 adds that the hook isn't killed, a latedenyis discarded, and parallel tool calls queue serially. The adapter needs its own deadlines well undertimeoutSec, and the README should say Copilot isn't a fail-closed boundary under load..claude/settings.json. In a repo with the Claude Code shim installed, Copilot may already run it through its Claude-compatible format. The shim requires ahook_event_namefield the reference doesn't list for that format, so it may exit 2 and deny every call. With both registered, a call could reach the Guardian twice.askand MODIFY involve the user.askbecomesdenyin the cloud agent and autopilot, and #3042 reports two confirmations perask.updatedInputrewrites prompt on every call (#2643);modifiedArgsneeds testing.localhostisn't reachable.~/.copilot/hooks/keeps it CLI-only.I am not entirely sure how to approach the copilot desktop application yet, but I will tackle that when we get there.
Because of @bar-capsule grinding out the cursor/claude code adapters etc. we should know how to tackle these because we have a provider agnostic methodology already.