feat(llm): add GitHub Copilot as LLM provider (#1512)

* Add github copilot as LLM provider.

* Fix Copilot in Openclaw

* security: harden Copilot OAuth token handling

C1: Use secrecy::SecretString for oauth_token and cached session token
    in CopilotTokenManager/CachedCopilotToken. Expose only at HTTP
    header injection point via .expose_secret().

C2: Document risks of hardcoded VS Code OAuth client ID and editor
    identity headers (ToS, rotation, staleness). Remove the unreliable
    paste-token setup path (setup_github_copilot_manual_token).

C3: Fix TOCTOU race in get_token() — re-check token validity after
    acquiring write lock so concurrent callers don't all perform
    redundant token exchanges.

I1: Remove dead empty else {} block in get_token().

I2: Map 401 responses to LlmError::AuthFailed instead of RequestFailed
    so retry/circuit-breaker logic handles auth failures correctly.

I3: Replace prepare_github_copilot_setup() with call to existing
    set_llm_backend_preserving_model() helper to avoid logic drift.

I4: Add unit tests for CopilotTokenManager (caching, invalidation,
    expiry/buffer behavior), poll response parsing (all OAuth device
    flow states), and DeviceCodeResponse/CopilotTokenResponse deserialization.

Co-authored-by: Copilot <[email protected]>

* fix: address review feedback and code improvements (takeover #1202)

- Fix ContentPart::Text being silently dropped in convert_messages
- Replace custom truncate_for_error with crate::util::floor_char_boundary
- Fix CLAUDE.md: accurately describe dedicated provider (not "OpenAI-compatible path")
- Fix "Github" -> "GitHub" capitalization in READMEs
- Add manual token paste option to setup wizard (not just device login)
- Fix missing extension_manager field in EngineContext (merge fixup)
- cargo fmt applied

Co-Authored-By: fallenwood <[email protected]>
Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

* fix: address PR review feedback for GitHub Copilot provider

- Plumb request_timeout_secs into GithubCopilotProvider (was hardcoded 120s)
- Forward stop_sequences to Copilot API via OpenAI `stop` field
- Skip empty text part in multimodal message conversion
- Improve paste-token wizard hint with specific file path guidance

Co-Authored-By: fallenwood <[email protected]>
Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

* fix: 401 retry, retryable token exchange errors, shared retry-after parsing

- Retry once inline on 401 after token invalidation (was returning
  AuthFailed immediately, guaranteeing user-visible failure)
- Map token exchange failures to RequestFailed (retryable) instead of
  AuthFailed (non-retryable by RetryProvider)
- Use shared crate::llm::retry::parse_retry_after for HTTP-date support
  and safe 60s default
- Improve paste-token wizard hint: mention `gh auth token` as primary source

Co-Authored-By: fallenwood <[email protected]>
Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

* fix: 401 retry error mapping, retry status logging, token whitespace safety

- Map 401 retry get_token() failure to RequestFailed (retryable),
  consistent with initial token acquisition path
- Log retry response status before returning AuthFailed
- Trim oauth_token in exchange_copilot_token to prevent header panics
  from whitespace in env vars

Co-Authored-By: fallenwood <[email protected]>
Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

---------

Co-authored-by: Fallenwood <[email protected]>
Co-authored-by: Copilot <[email protected]>
Co-authored-by: fallenwood <[email protected]>
Co-authored-by: Claude Opus 4.6 (1M context) <[email protected]>

tests/config_round_trip.rs

@@ -56,6 +56,7 @@ fn bootstrap_env_round_trips_llm_backend() {
     for backend in &[
         "nearai",
         "anthropic",
+        "github_copilot",
         "ollama",
         "openai_compatible",
         "tinfoil",