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## Problem
The handoff summarizer sends `max_tokens: 8192`
(`HANDOFF_MAX_OUTPUT_TOKENS`) with no reasoning budget separation. On
reasoning models, thinking tokens count against that cap: the model can
spend the entire budget reasoning, length-stop with empty `content`, and
`summarize()` — which only reads `content` — reports an empty summary.
The handoff then degrades to lossy history truncation.
Observed on deepseek-v4-flash during a terminal-bench 2.1 run
(tb21-solo-3, 89 tasks): **13 consecutive handoff attempts across 5
trials failed exactly this way** (`handoff returned empty summary;
truncating`), each burning ~3 minutes of full-cap reasoning, before a
stochastically-short reasoning run finally fit. circuit-fibsqrt alone: 5
failures, 5 truncations, then success on attempt 6. video-processing
failed its task by one frame after 3 context truncations.
## Fix
`openrouter_summary_body` now grants reasoning its own equal-sized
budget and excludes it from the response:
- `reasoning.max_tokens = max_output_tokens` — thinking gets a dedicated
budget instead of competing with the summary text
- `reasoning.exclude = true` — reasoning is never in the response body;
`summarize()` only reads `content`
- `max_tokens = max_output_tokens * 2` — the total cap covers both
budgets, so the text budget the caller asked for is actually available
for text
Non-reasoning endpoints ignore the `reasoning` object. Deliberately not
paired with `provider.require_parameters`, for the reasons documented at
`apply_openrouter_mutations` (it hard-404s valid model ids).
The prior test
`openrouter_summary_carries_neither_reasoning_nor_provider` asserted
`reasoning` absent from the summary body — that assertion guarded
against *effort-based* reasoning leaking in from config (the body is
built independently of `cfg`, which is still true and still tested:
`reasoning.effort` stays unset). Replaced with
`openrouter_summary_budgets_reasoning_separately_and_carries_no_provider`.
## Verification
- `cargo test -p buzz-agent`: 422 unit + 110 integration tests pass at
bb2fedde
- `cargo fmt` / `cargo clippy -p buzz-agent --all-targets`: clean
- Not yet validated against a live OpenRouter reasoning endpoint — the
failing scenario needs a long-context session to trigger organically.
Evidence for the mechanism is from run artifacts (13/13 empty-summary
length-stops on deepseek-v4-flash) and OpenRouter's documented
`reasoning.max_tokens`/`reasoning.exclude` semantics.
---------
Signed-off-by: Eva <011987e296fd5006292d2f930b574be47c7801048d1983c46c425d3c95f0cffd@buzz.block.builderlab.xyz>
Co-authored-by: Eva <011987e296fd5006292d2f930b574be47c7801048d1983c46c425d3c95f0cffd@buzz.block.builderlab.xyz>