Expose install_bundled_cli and HAS_BUNDLED_CLI in the Rust SDK

[tclem]

github-app's health panel (and any caller that always sets CliProgram::Path(...)) needs the bundled CLI's path before a Client exists, but embeddedcli::path() is pub(crate). github-app has had to reinvent the cache-path convention in its own health module, making four copies (build.rs, embeddedcli.rs, resolve.rs, and the consumer) that have to stay byte-for-byte in sync or runtime resolution silently breaks.

This lifts the existing extraction path to a stable public surface without adding new logic:

pub const HAS_BUNDLED_CLI: bool;
pub fn install_bundled_cli() -> Option<PathBuf>;

install_bundled_cli() wraps embeddedcli::path() and returns the same path Client::start resolves to for CliProgram::Resolve with no COPILOT_CLI_PATH and no ClientOptions::bundled_cli_extract_dir override. Lazy on first call, idempotent thereafter, None when the bundled-cli feature is off or the target isn't supported by build.rs.

Notes for reviewers

• No fallback to the dev-cache path. install_bundled_cli() returns None rather than chaining into the has_extracted_cli (bundled-cli off) branch. That's a separate question and callers can still reach it via CliProgram::Resolve. Consumer asked for this shape explicitly.
• HAS_BUNDLED_CLI keys off cfg(has_bundled_cli), not the feature flag. So it stays accurate on unsupported targets even when the feature is on, and callers can branch on bundling presence without forcing extraction.
• install_at stays pub(crate). No consumer needs the extract-dir variant today. If one shows up we can add install_bundled_cli_at(&Path) later.
• resolve.rs is untouched. Client::start still goes through embeddedcli::path() directly; the public wrapper is just another caller of the same function.

Companion consumer change is github/github-app#5834, which replaces its hand-rolled find_bundled_copilot_path plus the duplicated sdk_cli_cache_root / sanitize_cli_version / COPILOT_CLI_EXTRACT_DIR_ENV helpers with this single SDK call.

  _{Generated via Copilot (Claude Opus 4.7) on behalf of @tclem}

[Copilot]

Pull request overview

Exposes a stable public surface (HAS_BUNDLED_CLI constant and install_bundled_cli() function) at the Rust SDK crate root, so consumers like github-app can reach the bundled Copilot CLI path without constructing a Client, eliminating duplicated cache-path logic in downstream crates.

Changes:

• Add pub const HAS_BUNDLED_CLI (keyed on cfg(has_bundled_cli)) and pub fn install_bundled_cli() as a thin wrapper over the existing pub(crate) embeddedcli::path().
• Document the new surface in the README under "Embedded CLI resolution".
• Add integration tests covering both bundled (idempotent, matches resolver) and non-bundled (None, no dev-cache fallback) configurations.

Show a summary per file

File	Description
rust/src/lib.rs	Adds public HAS_BUNDLED_CLI const and install_bundled_cli() wrapper around the crate-private embedded CLI installer.
rust/README.md	Documents the new "reaching the bundled binary without a Client" pattern with a runnable snippet.
rust/tests/cli_resolution_test.rs	Adds three feature/cfg-gated tests: idempotent extraction, parity with Client::start resolver, and None when not bundled.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 0