Add copilot-relay usage: Copilot plan and quota

[D0n9X1n]

Summary

Adds copilot-relay usage [--json] (#154): the Copilot plan, SKU and quota reset date, then one line per quota, from GitHub's copilot_internal/user, requested with the stored GitHub token. No relay needs to run. It exchanges no Copilot token and writes no file, the log included.

• src/lib/auth.ts: getCopilotUsage sends the request with githubHeaders and the same fetch as the other GitHub calls in that file, so the [Feature]: Send Copilot and GitHub calls through an outbound proxy (upstreamProxy) #153 dispatcher change can move it with them. readStoredGitHubToken reads the token without creating a directory or file and without migrating a legacy token.
• src/lib/usage.ts: checks every field on its own (a missing or mistyped field counts as not reported), keeps only the plan and quota fields, makes each string terminal-safe, renders the report, and turns each failure into one line. It refuses an answer whose plan, SKU, reset date or quota ids would show the stored token: written exactly, with other characters inside it, or spread over those strings.
• src/usage.ts, registered in src/main.ts: prints to stdout and stderr and sets process.exitCode = 1 instead of throwing, because citty prints a thrown error with consola.error, which also writes the log file.
• src/lib/config.ts: exports vscodeVersion, so the request sends the editor version without readAppConfig, which can write config.yaml.

Text output, with placeholder values:

Plan         <copilot_plan>
SKU          <access_type_sku>
Quota reset  <quota_reset_date>

chat                  unlimited; overage not permitted, overage count <overage_count>
completions           unlimited; overage not permitted, overage count <overage_count>
premium_interactions  <remaining> of <entitlement> remaining (<percent_remaining>%); overage permitted, overage count <overage_count>

A quota with credits_used gets ; credits used <n> at the end. Values print as GitHub sent them; nothing is rounded or computed. A missing field prints ?; a missing plan, SKU, reset date or quota prints not reported. --json prints a curated object with the same fields, never the raw response. copilot_plan, access_type_sku, quota_reset_date and each known quota id are always present; a value, snapshot or field that is absent or mistyped is null; a snapshot object always has all eight keys.

Closes #154

Scope

A CLI command only: no HTTP route, no config key, and no change to the relay's request path.

Validation

• npm run typecheck
• npm run test:unit: 986 tests, 956 pass, 30 skipped (none new), 0 fail
• npm run test:integration: 402 tests, 402 pass, 0 fail
• npm run build

Run locally on Windows with Node 24.19.0. New tests: tests/unit/usage.test.ts (43) and tests/integration/usage-command.test.ts (9). Both mock fetch; nothing calls GitHub. The integration test runs the CLI in a child process against a temporary home and checks that nothing in it is created or changed.

Notes

• Token: read from ~/.copilot-relay/github_token and sent only in the authorization header. GitHub's answer and a network error's reason are checked for it before anything is printed: written exactly, with other characters between its letters and digits, or, in an answer, spread over the plan, SKU, reset date and quota ids. An exact copy in a reason prints as [redacted]; a reason that still spells the token prints Could not reach GitHub.; an answer that would show it is refused with one fixed line, and none of it is printed. The two looser forms are searched for only when the token has at least 16 letters and digits. A token written any other way, such as in another case or encoding, is not found.
• The request has a 30-second timeout with its own message.
• Logging: none; the command never calls the logger.
• Config: no change.

Checklist

• Public API remains Claude Code-only unless intentionally changed.
• Config changes are reflected in config.default.yaml, README, and wiki/ (EN and ZH). No config change; the command is documented in the README and in both wiki languages.
• Logs do not expose tokens.
• Integration tests mock upstream Copilot; they do not call real Copilot services.

After merge

• Confirm publish-wiki.yml succeeded on the merge SHA, then click through the new sections on the live EN and 中文 tabs.
• Remove inactive local/remote feature branches and temporary worktrees, prune stale refs, and report preserved work; follow the Development Wiki cleanup rules.

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