(WIP) feat: Implement Copilot CLI feature via ACP

.changeset/copilot-acp-provider.md

@@ -0,0 +1,5 @@
+---
+"helmor": patch
+---
+
+Add GitHub Copilot CLI as an agent provider via the Agent Client Protocol, with hybrid binary discovery, async image attachments, shared `.agents/skills` slash-command scanning, and accurate permission deny handling.

.changeset/copilot-model-selection.md

@@ -0,0 +1,5 @@
+---
+"helmor": patch
+---
+
+Copilot model picker now shows live models fetched from the ACP server instead of a static "Default" entry.

.changeset/copilot-models-and-modes.md

@@ -0,0 +1,9 @@
+---
+"helmor": patch
+---
+
+Bring GitHub Copilot to feature parity with Codex/Claude in the composer:
+- Model picker is now sourced live from Copilot's ACP `SessionModelState` and applied per turn via `unstable_setSessionModel`.
+- Plan mode and a Copilot-only Autopilot toggle drive ACP `setSessionMode` (interactive/plan/autopilot).
+- Context-window ring + usage status are wired from Copilot's `usage_update` notifications through the same persistence path as Codex.
+- Effort levels (low/medium/high/xhigh) are exposed on the static catalog entry.

sidecar/package.json

@@ -13,6 +13,7 @@
 		"typecheck": "bunx tsc --noEmit"
 	},
 	"dependencies": {
+		"@agentclientprotocol/sdk": "^0.21.0",
 		"@anthropic-ai/claude-agent-sdk": "0.2.126",
 		"@anthropic-ai/claude-code": "2.1.126",
 		"@cursor/sdk": "^1.0.12",

sidecar/src/context-usage.test.ts

@@ -3,6 +3,7 @@ import {
 	buildClaudeRichMeta,
 	buildClaudeStoredMeta,
 	buildCodexStoredMeta,
+	buildCopilotStoredMeta,
 } from "./context-usage";
 
 const CLAUDE_MODEL = "claude-opus-4-7[1m]";
@@ -377,3 +378,36 @@ describe("buildCodexStoredMeta", () => {
 		expect(meta?.modelId).toBe("");
 	});
 });
+
+describe("buildCopilotStoredMeta", () => {
+	it("maps used/size into the persisted meta shape", () => {
+		const meta = buildCopilotStoredMeta(
+			{ used: 12_000, size: 200_000 },
+			"claude-sonnet-4.6",
+		);
+		expect(meta).toEqual({
+			modelId: "claude-sonnet-4.6",
+			usedTokens: 12_000,
+			maxTokens: 200_000,
+			percentage: 6,
+		});
+	});
+
+	it("clamps used to size when ACP over-reports", () => {
+		const meta = buildCopilotStoredMeta(
+			{ used: 250_000, size: 200_000 },
+			"copilot-default",
+		);
+		expect(meta?.usedTokens).toBe(200_000);
+		expect(meta?.percentage).toBe(100);
+	});
+
+	it("falls back to a stable model id when ACP hasn't reported one", () => {
+		const meta = buildCopilotStoredMeta({ used: 500, size: 100_000 }, null);
+		expect(meta?.modelId).toBe("copilot");
+	});
+
+	it("returns null when both fields are zero", () => {
+		expect(buildCopilotStoredMeta({ used: 0, size: 0 }, null)).toBeNull();
+	});
+});

sidecar/src/context-usage.ts

@@ -180,3 +180,27 @@ export function buildCodexStoredMeta(
 		percentage: computePercentage(usedClamped, max),
 	};
 }
+
+/**
+ * Build the persisted meta from a Copilot ACP `usage_update` session
+ * notification. ACP exposes raw `used` / `size` token counts (size =
+ * full context window). When the active session hasn't reported a
+ * model id yet (e.g. older Copilot CLI builds without
+ * `SessionModelState`), fall back to the constant `"copilot"` so the
+ * UI ring still renders.
+ */
+export function buildCopilotStoredMeta(
+	usage: { used?: number | null; size?: number | null },
+	modelId: string | null,
+): StoredContextUsageMeta | null {
+	const used = num(usage.used);
+	const max = num(usage.size);
+	if (used <= 0 && max <= 0) return null;
+	const usedClamped = max > 0 ? Math.min(used, max) : used;
+	return {
+		modelId: modelId ?? "copilot",
+		usedTokens: usedClamped,
+		maxTokens: max,
+		percentage: computePercentage(usedClamped, max),
+	};
+}

sidecar/src/copilot-acp-session-manager.test.ts

@@ -0,0 +1,6 @@
+import { expect, test } from "bun:test";
+import { COPILOT_ACP_ARGS } from "./copilot-acp-session-manager.js";
+
+test("Copilot ACP uses the supported top-level --acp flag", () => {
+	expect(COPILOT_ACP_ARGS).toEqual(["--acp"]);
+});