Add CompressionFailurePolicy so a summarizer error no longer aborts the run

[M3gA-Mind]

ContextCompressionMiddleware propagated a Summarizer error through before_model, aborting the whole run — precisely on the longest transcripts that reached the compaction threshold. The default ConcatSummarizer can't fail, so the gap was invisible in tests, but the trait allows Err.

This adds a CompressionFailurePolicy (Abort | FallbackTrim | PassThrough) on the middleware, defaulting to a deterministic front-drop trim to the policy's trigger budget (system messages preserved) and emitting a MiddlewareFailed diagnostic on fallback. Tests cover all three policies with a failing summarizer.

Commands run: cargo fmt, cargo test --lib (998 passed), cargo clippy --lib --tests -- -D warnings (clean for this change). Note: there is one pre-existing, unrelated clippy collapsible_if denial in src/harness/model/mod.rs from the current HEAD (#34), surfaced only by newer clippy; left untouched to keep this change focused.

Closes tinyhumansai/openhuman#4640

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📥 Commits

Reviewing files that changed from the base of the PR and between b1f0d82 and 1e9e515.

📒 Files selected for processing (5)

• src/harness/middleware/library/context.rs
• src/harness/middleware/test.rs
• src/harness/middleware/types.rs
• src/harness/model/mod.rs
• src/harness/stream/mod.rs

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[M3gA-Mind]

CI guardian: the Rust SDK check was red on a pre-existing main clippy failure under stable rust 1.96 (a collapsible_if in StreamAccumulator::push_tool_chunk and a duplicated #[cfg(test)] on the stream test module), inherited by this branch. Pushed a behavior-neutral lint fix so CI can go green; no change to this PR's own logic.