[Bug]: dead_code warning for fork_session_for_plugin in feature-less core test builds

[1688mengdie]

Summary

The upstream CI logs for main report a dead-code warning for fork_session_for_plugin in bitfun-core. Evidence from GitHub Actions run 33035362609 — job "CLI Tests (ubuntu-latest)" and "CLI Tests (macos-15)" (also present in runs 33050974141 and 33047041028):

• warning: function fork_session_for_plugin is never used --> src/crates/assembly/core/src/product_runtime.rs:614:21

Cross-checking the crate: the only consumer of CoreProductAgentRuntime::fork_session_for_plugin is the plugin host HTTP routes implementation (plugin_host_http_routes_impl.rs), which is compiled under the opencode-plugin-host feature gate in the crate's lib.rs. Test builds that do not enable that feature — notably the sdk-host test compilation unit used by the CLI Tests jobs — therefore see a function with zero callers and report it as dead code.

Root Cause Analysis

• The function is plugin-host-only by construction, but its declaration is unconditional. The crate's feature gate already scopes its sole consumer; the declaration itself was not scoped, so any build without opencode-plugin-host (including the sdk-host test unit on ubuntu/macos) flags it as dead_code. The warning is structural: every full CI run with the ubuntu/macos test units reproduces it.

Proposed Fix

Gate the function with #[cfg(feature = "opencode-plugin-host")] at its declaration in product_runtime.rs, so:

• feature-less test builds (sdk-host test unit) stop emitting the dead-code warning;
• the plugin-host build keeps the function available for its single consumer.

No #[allow(dead_code)] suppression is involved.