5 files changed, 384 insertions, 11 deletions

diff --git a/packages/core/src/credentials/claude.ts b/packages/core/src/credentials/claude.ts
index 7818222..050a0fc 100644
--- a/packages/core/src/credentials/claude.ts
+++ b/packages/core/src/credentials/claude.ts
@@ -441,6 +441,22 @@ export interface ClaudeUsageReport {
 	orgId?: string;
 }
 
+/**
+ * A usage report paired with provenance: whether it came back from a fresh
+ * live fetch against Anthropic's `/api/oauth/usage` endpoint or was served
+ * from the local `usage_cache` table after a failed/skipped live fetch.
+ *
+ * `source: "cache"` carries `cachedAt` — the epoch-ms timestamp recording when
+ * that cached payload was last fetched FROM the source (the `usage_cache.cached_at`
+ * column). `source: "live"` omits `cachedAt` (the data is current as of now).
+ */
+export interface ClaudeUsageResult {
+	report: ClaudeUsageReport;
+	source: "live" | "cache";
+	/** Epoch-ms the cached report was last fetched from source. Only on `source: "cache"`. */
+	cachedAt?: number;
+}
+
 // ─── Well-known Anthropic models ──────────────────────────────
 
 /**
@@ -602,14 +618,23 @@ async function fetchClaudeUsage(accessToken: string): Promise<ClaudeUsageReport
 	}
 }
 
-function getCachedUsage(keyId: string): ClaudeUsageReport | null {
+/**
+ * Read a cached usage report plus the epoch-ms it was last fetched from source.
+ * Returns `null` when there is no cached row (or on any DB/parse error).
+ */
+function getCachedUsageWithMeta(
+	keyId: string,
+): { report: ClaudeUsageReport; cachedAt: number } | null {
 	try {
 		const db = getDatabase();
 		const row = db
-			.query("SELECT report_json FROM usage_cache WHERE key_id = $keyId")
-			.get({ $keyId: keyId }) as { report_json: string } | null;
+			.query("SELECT report_json, cached_at FROM usage_cache WHERE key_id = $keyId")
+			.get({ $keyId: keyId }) as { report_json: string; cached_at: number } | null;
 		if (!row) return null;
-		return JSON.parse(row.report_json) as ClaudeUsageReport;
+		return {
+			report: JSON.parse(row.report_json) as ClaudeUsageReport,
+			cachedAt: row.cached_at,
+		};
 	} catch {
 		return null;
 	}
@@ -635,13 +660,35 @@ function setCachedUsage(keyId: string, provider: string, report: ClaudeUsageRepo
 	}
 }
 
-export async function getAccountUsage(account: ClaudeAccount): Promise<ClaudeUsageReport | null> {
+/**
+ * Fetch an account's usage report along with its provenance (live vs cache).
+ *
+ * Resolution: refresh credentials and hit the live `/api/oauth/usage` endpoint;
+ * on success the fresh report is cached and returned as `source: "live"`. If
+ * credentials cannot be refreshed OR the live fetch returns nothing, fall back
+ * to the local `usage_cache` row and return it as `source: "cache"` with the
+ * `cachedAt` timestamp recording when that payload was last fetched from source.
+ * Returns `null` only when neither a live report nor a cached row is available.
+ */
+export async function getAccountUsageWithSource(
+	account: ClaudeAccount,
+): Promise<ClaudeUsageResult | null> {
 	const creds = await refreshAccountCredentialsAsync(account);
-	if (!creds) return getCachedUsage(account.id);
-	const report = await fetchClaudeUsage(creds.accessToken);
-	if (report) {
-		setCachedUsage(account.id, "anthropic", report);
-		return report;
+	if (creds) {
+		const report = await fetchClaudeUsage(creds.accessToken);
+		if (report) {
+			setCachedUsage(account.id, "anthropic", report);
+			return { report, source: "live" };
+		}
 	}
-	return getCachedUsage(account.id);
+	const cached = getCachedUsageWithMeta(account.id);
+	if (cached) {
+		return { report: cached.report, source: "cache", cachedAt: cached.cachedAt };
+	}
+	return null;
+}
+
+export async function getAccountUsage(account: ClaudeAccount): Promise<ClaudeUsageReport | null> {
+	const result = await getAccountUsageWithSource(account);
+	return result?.report ?? null;
 }
diff --git a/packages/core/src/credentials/index.ts b/packages/core/src/credentials/index.ts
index 5221dc6..131f035 100644
--- a/packages/core/src/credentials/index.ts
+++ b/packages/core/src/credentials/index.ts
@@ -15,9 +15,11 @@ export {
 	type ClaudeProfile,
 	type ClaudeUsageBucket,
 	type ClaudeUsageReport,
+	type ClaudeUsageResult,
 	discoverClaudeAccounts,
 	fetchAnthropicModels,
 	getAccountUsage,
+	getAccountUsageWithSource,
 	getAnthropicBetas,
 	getAnthropicHeaders,
 	getClaudeAccountsFromDB,
diff --git a/packages/core/src/index.ts b/packages/core/src/index.ts
index 50012f1..f58209f 100644
--- a/packages/core/src/index.ts
+++ b/packages/core/src/index.ts
@@ -116,6 +116,7 @@ export {
 } from "./skills/index.js";
 export { prefix as bashArityPrefix } from "./tools/bash-arity.js";
 // Tools
+export { createKeyUsageTool, type KeyUsageCallbacks } from "./tools/key-usage.js";
 export { createListFilesTool } from "./tools/list-files.js";
 export { createLspTool, type LspToolContext } from "./tools/lsp.js";
 export { createReadFileTool } from "./tools/read-file.js";
diff --git a/packages/core/src/tools/key-usage.ts b/packages/core/src/tools/key-usage.ts
new file mode 100644
index 0000000..0655ad7
--- /dev/null
+++ b/packages/core/src/tools/key-usage.ts
@@ -0,0 +1,322 @@
+import { z } from "zod";
+import type { ClaudeAccount, ClaudeUsageReport, ClaudeUsageResult } from "../credentials/claude.js";
+import { getAccountUsageWithSource } from "../credentials/claude.js";
+import type { OpencodeUsageReport } from "../credentials/opencode.js";
+import { fetchOpencodeUsage as defaultFetchOpencodeUsage } from "../credentials/opencode.js";
+import type { KeyState, ToolDefinition } from "../types/index.js";
+
+/**
+ * Collaborators the `key_usage` tool needs from the API layer (which owns the
+ * live `ModelRegistry` and the discovered Claude accounts). The two `fetch*`
+ * hooks default to the real credential fetchers but are injectable so tests can
+ * exercise the tool without network or DB access.
+ */
+export interface KeyUsageCallbacks {
+	/** Current key states from the model registry (definition + active/exhausted status). */
+	listKeys(): KeyState[];
+	/** Discovered Claude accounts, used to resolve `anthropic` keys to credentials. */
+	listClaudeAccounts(): ClaudeAccount[];
+	/**
+	 * Fetch an anthropic account's usage with provenance (live vs cache).
+	 * Defaults to `getAccountUsageWithSource`.
+	 */
+	fetchAnthropicUsage?: (account: ClaudeAccount) => Promise<ClaudeUsageResult | null>;
+	/**
+	 * Fetch an opencode-go key's usage (always a live scrape — OpenCode keeps no
+	 * local cache). Defaults to `fetchOpencodeUsage`.
+	 */
+	fetchOpencodeUsage?: (keyId: string) => Promise<OpencodeUsageReport | null>;
+}
+
+/** A single normalized usage window (5-hour / week / month). */
+interface UsageWindow {
+	label: string;
+	/** Remaining headroom as a 0–100 percentage. Omitted when the source gives no utilization. */
+	remainingPercent?: number;
+	/** Epoch-ms the window resets. Omitted when the source gives no reset time. */
+	resetsAt?: number;
+}
+
+/** Fully normalized per-key usage, ready for rendering. */
+interface KeyUsageEntry {
+	keyId: string;
+	provider: string;
+	status: "active" | "exhausted";
+	lastError?: string;
+	exhaustedAt?: number;
+	/** Provenance of the usage figures: a fresh live fetch or a cached payload. */
+	dataSource?: "live" | "cache";
+	/** Epoch-ms the cached payload was last fetched from source (only on `dataSource: "cache"`). */
+	cachedAt?: number;
+	windows: UsageWindow[];
+	/** Set when no usage figures could be obtained for an otherwise-supported key. */
+	unavailableReason?: string;
+	/** Set when the provider has no usage-reporting support. */
+	unsupported?: boolean;
+}
+
+function clampPercent(value: number): number {
+	if (value < 0) return 0;
+	if (value > 100) return 100;
+	return value;
+}
+
+/** Convert a raw `{ utilization, resetsAt }` bucket into a normalized window. */
+function toWindow(
+	label: string,
+	bucket?: { utilization?: number; resetsAt?: number },
+): UsageWindow | null {
+	if (!bucket) return null;
+	const hasUtil = typeof bucket.utilization === "number";
+	const hasReset = typeof bucket.resetsAt === "number";
+	if (!hasUtil && !hasReset) return null;
+	return {
+		label,
+		...(hasUtil
+			? { remainingPercent: clampPercent(Math.round((1 - (bucket.utilization as number)) * 100)) }
+			: {}),
+		...(hasReset ? { resetsAt: bucket.resetsAt } : {}),
+	};
+}
+
+function anthropicWindows(report: ClaudeUsageReport): UsageWindow[] {
+	const windows: UsageWindow[] = [];
+	const fiveHour = toWindow("5-hour", report.fiveHour);
+	if (fiveHour) windows.push(fiveHour);
+	const week = toWindow("week", report.sevenDay);
+	if (week) windows.push(week);
+	return windows;
+}
+
+function opencodeWindows(report: OpencodeUsageReport): UsageWindow[] {
+	const windows: UsageWindow[] = [];
+	const fiveHour = toWindow("5-hour", report.fiveHour);
+	if (fiveHour) windows.push(fiveHour);
+	const week = toWindow("week", report.weekly);
+	if (week) windows.push(week);
+	const month = toWindow("month", report.monthly);
+	if (month) windows.push(month);
+	return windows;
+}
+
+/**
+ * Resolve which Claude account backs an `anthropic` key. Matches by key id or by
+ * the account's source file (the key's `credentials_file`), falling back to the
+ * first available account — mirrors the existing `/models/key-usage` route.
+ */
+function matchAnthropicAccount(
+	accounts: ClaudeAccount[],
+	keyId: string,
+	credFile?: string,
+): ClaudeAccount | undefined {
+	const matched = accounts.find(
+		(a) => a.id === keyId || (credFile != null && a.source === credFile),
+	);
+	return matched ?? accounts[0];
+}
+
+function iso(ms: number): string {
+	return new Date(ms).toISOString();
+}
+
+/** Human-readable coarse duration, e.g. "3h 12m", "5d 8h", "0m". */
+function formatDuration(ms: number): string {
+	const totalSec = Math.round(Math.abs(ms) / 1000);
+	const days = Math.floor(totalSec / 86400);
+	const hours = Math.floor((totalSec % 86400) / 3600);
+	const minutes = Math.floor((totalSec % 3600) / 60);
+	const parts: string[] = [];
+	if (days > 0) parts.push(`${days}d`);
+	if (hours > 0) parts.push(`${hours}h`);
+	if (minutes > 0 || parts.length === 0) parts.push(`${minutes}m`);
+	return parts.join(" ");
+}
+
+function formatRelative(targetMs: number, nowMs: number): string {
+	const delta = targetMs - nowMs;
+	return delta >= 0 ? `in ${formatDuration(delta)}` : `${formatDuration(delta)} ago`;
+}
+
+function formatWindow(window: UsageWindow, now: number): string {
+	const parts: string[] = [];
+	if (typeof window.remainingPercent === "number") {
+		parts.push(`${window.remainingPercent}% remaining`);
+	}
+	if (typeof window.resetsAt === "number") {
+		parts.push(`resets ${iso(window.resetsAt)} (${formatRelative(window.resetsAt, now)})`);
+	}
+	return `${window.label}: ${parts.join(", ")}`;
+}
+
+/**
+ * Render normalized usage entries into an AI-friendly text block. Pure — `now`
+ * is injected so relative timestamps are deterministic under test.
+ */
+export function formatKeyUsage(entries: KeyUsageEntry[], now: number): string {
+	if (entries.length === 0) return "No API keys matched.";
+
+	const lines: string[] = [];
+	lines.push(`API key usage — ${entries.length} key${entries.length === 1 ? "" : "s"}:`);
+
+	for (const entry of entries) {
+		lines.push("");
+		lines.push(`[${entry.keyId}] provider: ${entry.provider}`);
+
+		if (entry.status === "exhausted") {
+			const since =
+				typeof entry.exhaustedAt === "number"
+					? ` (since ${iso(entry.exhaustedAt)}, ${formatRelative(entry.exhaustedAt, now)})`
+					: "";
+			lines.push(`status: EXHAUSTED${since}`);
+			if (entry.lastError) lines.push(`last error: ${entry.lastError}`);
+		} else {
+			lines.push("status: active");
+		}
+
+		if (entry.unsupported) {
+			lines.push(
+				`usage: not supported for provider "${entry.provider}" (only anthropic and opencode-go report usage)`,
+			);
+			continue;
+		}
+
+		if (entry.dataSource === "live") {
+			lines.push("data: live (fetched just now)");
+		} else if (entry.dataSource === "cache") {
+			lines.push(
+				typeof entry.cachedAt === "number"
+					? `data: cached — last fetched from source ${iso(entry.cachedAt)} (${formatRelative(entry.cachedAt, now)})`
+					: "data: cached (source timestamp unknown)",
+			);
+		}
+
+		for (const window of entry.windows) {
+			lines.push(formatWindow(window, now));
+		}
+
+		if (entry.unavailableReason) {
+			lines.push(`usage: unavailable — ${entry.unavailableReason}`);
+		}
+	}
+
+	return lines.join("\n");
+}
+
+async function buildEntry(
+	key: KeyState,
+	accounts: ClaudeAccount[],
+	fetchAnthropic: (account: ClaudeAccount) => Promise<ClaudeUsageResult | null>,
+	fetchOpencode: (keyId: string) => Promise<OpencodeUsageReport | null>,
+): Promise<KeyUsageEntry> {
+	const def = key.definition;
+	const entry: KeyUsageEntry = {
+		keyId: def.id,
+		provider: def.provider,
+		status: key.status,
+		windows: [],
+		...(key.lastError ? { lastError: key.lastError } : {}),
+		...(typeof key.exhaustedAt === "number" ? { exhaustedAt: key.exhaustedAt } : {}),
+	};
+
+	if (def.provider === "anthropic") {
+		const account = matchAnthropicAccount(accounts, def.id, def.credentials_file);
+		if (!account) {
+			entry.unavailableReason = "no Claude account credentials available for this key";
+			return entry;
+		}
+		let result: ClaudeUsageResult | null = null;
+		try {
+			result = await fetchAnthropic(account);
+		} catch {
+			result = null;
+		}
+		if (!result) {
+			entry.unavailableReason = "no live usage data and no cached usage available";
+			return entry;
+		}
+		entry.dataSource = result.source;
+		if (typeof result.cachedAt === "number") entry.cachedAt = result.cachedAt;
+		entry.windows = anthropicWindows(result.report);
+		if (entry.windows.length === 0) {
+			entry.unavailableReason = "usage endpoint returned no window data";
+		}
+		return entry;
+	}
+
+	if (def.provider === "opencode-go") {
+		let report: OpencodeUsageReport | null = null;
+		try {
+			report = await fetchOpencode(def.id);
+		} catch {
+			report = null;
+		}
+		if (!report) {
+			entry.unavailableReason =
+				"live usage unavailable (requires OPENCODE_COOKIE and a workspace id, or the source returned no data; OpenCode keeps no local cache)";
+			return entry;
+		}
+		entry.dataSource = "live";
+		entry.windows = opencodeWindows(report);
+		if (entry.windows.length === 0) {
+			entry.unavailableReason = "usage source returned no window data";
+		}
+		return entry;
+	}
+
+	entry.unsupported = true;
+	return entry;
+}
+
+export function createKeyUsageTool(callbacks: KeyUsageCallbacks): ToolDefinition {
+	const fetchAnthropic = callbacks.fetchAnthropicUsage ?? getAccountUsageWithSource;
+	const fetchOpencode = callbacks.fetchOpencodeUsage ?? defaultFetchOpencodeUsage;
+
+	return {
+		name: "key_usage",
+		description: [
+			"Report current usage levels for configured API keys so you can pick a key with",
+			"headroom, warn before hitting a rate limit, or diagnose an exhausted-key failure.",
+			"",
+			"For each key it returns: provider, active/exhausted status (with the last error when",
+			"exhausted), remaining rate-limit headroom per window (5-hour, weekly, and monthly where",
+			"the provider exposes it), each window's reset timestamp, and whether the figures are",
+			"live or served from cache (with the cache's last-fetched time).",
+			"",
+			"Pass a key_id to inspect one key; omit it to report all keys. Usage reporting is",
+			"supported for anthropic and opencode-go keys.",
+		].join("\n"),
+		parameters: z.object({
+			key_id: z
+				.string()
+				.optional()
+				.describe(
+					'The id of a single key to report (as configured in dispatch.toml, e.g. "claude-max"). Omit to report all configured keys.',
+				),
+		}),
+		execute: async (args: Record<string, unknown>): Promise<string> => {
+			const requestedKeyId = (args.key_id as string | undefined)?.trim() || undefined;
+
+			const allKeys = callbacks.listKeys();
+			if (allKeys.length === 0) {
+				return "No API keys are configured.";
+			}
+
+			let keys = allKeys;
+			if (requestedKeyId) {
+				keys = allKeys.filter((k) => k.definition.id === requestedKeyId);
+				if (keys.length === 0) {
+					const available = allKeys.map((k) => k.definition.id).join(", ");
+					return `Error: no key found with id "${requestedKeyId}". Available keys: ${available}.`;
+				}
+			}
+
+			const accounts = callbacks.listClaudeAccounts();
+			const entries: KeyUsageEntry[] = [];
+			for (const key of keys) {
+				entries.push(await buildEntry(key, accounts, fetchAnthropic, fetchOpencode));
+			}
+
+			return formatKeyUsage(entries, Date.now());
+		},
+	};
+}
diff --git a/packages/core/src/tools/summon.ts b/packages/core/src/tools/summon.ts
index b941152..2a076e6 100644
--- a/packages/core/src/tools/summon.ts
+++ b/packages/core/src/tools/summon.ts
@@ -287,6 +287,7 @@ export function createSummonTool(
 					"write_file",
 					"run_shell",
 					"search_code",
+					"key_usage",
 					"todo",
 					"summon",
 					"retrieve",