feat(usage): migrate usage fetchers to plugin sources

Serve the legacy usage RPC from discovered source reports so older apps retain the same host usage list while new clients use the source registry. Keep credential reads and normalization inside each source.

docs/glossary.md

@@ -31,6 +31,8 @@ Authoritative terminology. UI label wins. Don't invent synonyms; use what's here
 - **Agent profile** — A named launch bundle: provider, model, mode, thinking option, feature values, and free-text notes. Applying one writes those values into the **Agent controls** and is then forgotten — there is no selected profile, no default profile, and no drift tracking. The notes are written for orchestrating agents and are what the `list_profiles` MCP tool surfaces. Stored host-wide in daemon config as `agentProfiles`. UI: "Agent profiles". Code: `AgentProfile` (`packages/protocol/src/messages.ts:161`). Carries no system prompt, because a per-agent system prompt can only be set at creation. Forbidden: "Favourite", which this replaced.
 - **Terminal profile** — A named shell command a terminal can launch. Stored host-wide in daemon config as `terminalProfiles`. UI: "Terminal profiles". Code: `TerminalProfile` (`packages/protocol/src/messages.ts:135`), `resolveTerminalProfiles` (`packages/protocol/src/terminal-profiles.ts`). Also selectable as a New Workspace launch target, where the alternative is the chat agent.
 - **Provider** — Agent backend (Claude Code, Codex, Copilot, OpenCode, Pi, Oh My Pi). UI: "Provider". Code: `ProviderSnapshotEntry` (`packages/protocol/src/messages.ts:198`).
+- **Usage source** — Plugin registration that discovers accounts and fetches plan usage. Code: `UsageSourceRegistration` (`packages/plugin/src/server/usage.ts`).
+- **Usage report** — A source's normalized usage for one account, including status and optional windows, balances, and details. Code: `UsageReport` (`packages/plugin/src/server/usage.ts`).
 - **Model** — A specific LLM offered by a provider. UI: "Model" / "Select model". Code: `AgentModelDefinition` (`packages/protocol/src/messages.ts:187`).
 - **Tab** — UI surface representing one session inside a workspace. Not a conceptual unit; use **Agent session** when talking about the model. Code: `WorkspaceTabDescriptor` (`packages/app/src/screens/workspace/workspace-tabs-types.ts`).
 - **Terminal** — Workspace-scoped PTY shell streamed over the binary mux channel. UI: "Terminal". Code: `TerminalStreamFrame` (`packages/protocol/src/terminal-stream-protocol.ts`).

docs/plugins.md

@@ -376,6 +376,12 @@ external `href` or `xlink:href` references are rejected. Fragment references suc
 allowed. Paseo reads and sanitizes the file when the plugin starts; the string is never an inline
 SVG or URL.
 
+## Usage sources
+
+Register a usage source from `index.server.ts` with `server.registerUsageSource()`. Import `UsageSourceRegistration` and normalization helpers from `@getpaseo/plugin/server/usage`. `input` is a Zod schema checked inside the plugin process before `fetch(input)` runs. `discover()` returns the inputs for accounts found on the host; an empty list omits the source from host usage. `fetch()` returns a report with a stable `account.key` so the daemon can deduplicate accounts and cache by source and input. A failed input or fetch becomes an error report for that source. `icon` uses the same sanitized SVG file rules as provider icons.
+
+The daemon calls discovery for `usage.list_reports`; the client gates this RPC on `server_info.features.usageSources`. The old `provider.usage.list` RPC maps discovered reports for older clients. See the [public usage source reference](../public-docs/plugins/reference.md#usage-sources) for the author contract and minimum version.
+
 ## Contribute buttons
 
 Header buttons and composer pills share the client-only descriptor and registration lifecycle in

docs/providers.md

@@ -195,26 +195,17 @@ promise for completion: equal results, including equal discovery timestamps, emi
 
 ---
 
-## Provider Usage Fetchers
+## Usage sources
 
-Provider plan usage is fetch-on-demand, not a daemon push subscription. The app calls `provider.usage.list.request` through React Query when the usage tooltip or Host Usage settings screen is shown, and the daemon returns the normalized `ProviderUsage` list directly.
+Usage is fetched on demand from plugin usage sources. Each source registers through `server.registerUsageSource()` with an input schema, `fetch(input)`, and optional `discover()`. The daemon discovers configured accounts, validates inputs in the plugin process, caches each source/input result for five minutes, and returns `usage.list_reports.response`. A source report has an account key, availability status, plan label, windows, balances, and details. Mark the window the app should show first with `headline: true`.
 
-To add plan usage for a provider, add `packages/server/src/services/quota-fetcher/providers/<provider>.ts` and register it in `packages/server/src/services/quota-fetcher/manifest.ts`. The provider file exports only its fetcher class; provider auth, endpoint constants, API schemas, and normalization helpers stay private in that file. A fetcher owns provider auth/API parsing and returns the generic shape:
+Create an internal source under `packages/server/src/plugins/<name>-usage-source/` with the same manifest, entry, `server/`, `shared/`, and `icon.svg` layout as an external plugin. Register internal sources in `packages/server/src/plugins/index.ts`. Keep credential discovery, API parsing, and normalization inside the source; use helpers from `@getpaseo/plugin/server/usage`. The wire shape remains source agnostic. See [plugin usage sources](plugins.md#usage-sources).
 
-- `providerId`, `displayName`, `status`, and optional `planLabel`
-- any number of `windows` such as Session, Weekly, or Biweekly
-- optional `balances` for credits, USD, requests, or tokens
-- optional `details` for provider-specific rows
+`provider.usage.list` remains a compatibility RPC for older apps. It maps discovered reports to `ProviderUsage`. New clients use `usage.list_reports` after checking `server_info.features.usageSources`.
 
-Keep the protocol shape provider-agnostic. Do not add provider-specific renderers for new limit windows; labels and generic bars should carry the UI. API responses should be parsed and normalized with Zod inside the fetcher, while the protocol boundary stays strict so old/new client compatibility is explicit.
+### Credentials are read only
 
-Kimi Code usage follows the CLI-managed credential file at `KIMI_CODE_HOME` or `~/.kimi-code/credentials/kimi-code.json`; do not probe the legacy `~/.kimi` path as the primary source for current Kimi Code installs.
-
-Cursor usage reads the desktop `state.vscdb` token first, then `cursor-agent`'s `~/.config/cursor/auth.json`. Headless hosts only have the CLI file.
-
-### Usage fetchers are read-only on credentials
-
-A fetcher reads the provider's credential file and never writes it. On a 401 or 403 it returns `unavailable` and leaves refresh to the provider's own CLI: redeeming a refresh token in the fetcher invalidates the CLI's copy (refresh tokens are single-use), and rewriting the file through the fetcher's Zod schema drops any field the schema does not model, corrupting the file for the CLI.
+A source reads provider credentials without writing them. On 401 or 403 it returns `unavailable` and leaves refresh to the provider CLI. Redeeming a refresh token here would invalidate the CLI's copy; rewriting a parsed credential file could drop fields the source does not model.
 
 ---