[Bugfix] Fix Gemma4 streaming tool calls lost when entire call arrives in one delta

[alexbi29]

Summary

Fixes five coupled bugs that caused Gemma4 streaming tool calls to be silently dropped and the raw <|tool_call>...<tool_call|> / <|channel>thought... text to leak to downstream consumers (e.g. Telegram messages from an OpenClaw agent).

Reproduces with --stream-interval 20 (or any value ≥ the length of the tool call in tokens), which batches all generated tokens into a single SSE chunk.

---

Bug 1 — is_reasoning_end returns False when <|tool_response> precedes <|tool_call> in the same delta

File: vllm/reasoning/gemma4_reasoning_parser.py

With stream-interval batching the full sequence arrives in one delta:

<|channel>(100)  thought\n(45518) \n(107)  <channel|>(101)
<|tool_call>(48)  …args…  <tool_call|>(49)  <|tool_response>(50, stop)

is_reasoning_end searches the token list from the end. It hit <|tool_response> (id 50) first and returned False — preventing state.reasoning_ended from ever being set. DelegatingParser.parse_delta therefore never entered the tool-call phase; the reasoning parser returned the raw tool-call text as content and it leaked downstream.

Fix: Change <|tool_response> from return False to continue so the search reaches the preceding <|tool_call> token and correctly returns True.

---

Bug 2 — _extract_streaming Case 2 skipped when start and end tokens arrive together

File: vllm/tool_parsers/gemma4_tool_parser.py

Once the tool-call phase is entered (after Bug 1 is fixed), extract_tool_calls_streaming receives current_text = "<|tool_call>call:exec{…}<tool_call|>" with previous_text = "".

_extract_streaming computes start_count = end_count = 1. Case 2 required start_count > end_count (false when equal), so tool state was never initialised. Case 3 then called _handle_tool_call_end with current_tool_id = -1 → None. prev_tool_call_arr stayed empty → auto_tools_called = False → finish_reason = "stop" instead of "tool_calls".

Fix: Remove and start_count > end_count from Case 2 and update _handle_tool_call_end to emit name + full arguments together in the single-delta path.

---

Bug 3 — DelegatingParser.parse_delta drops reasoning when reasoning ends and tool call begins in the same delta

File: vllm/parser/abstract_parser.py

Closes #39885.

Even after Bugs 1 and 2 are fixed, the reasoning extracted by extract_reasoning_streaming() is silently discarded. parse_delta stores the result in delta_message, then unconditionally overwrites it with the return value of _extract_tool_calls_streaming(). The reasoning field is never forwarded to the client — reasoning_content is always null for the single-delta case.

This is what causes <|channel>thought\n…<channel|> to appear verbatim in the dialog of agentic harnesses: the client sees no reasoning_content and falls back to displaying raw content.

Sequence in the single-delta case:

1. extract_reasoning_streaming() returns DeltaMessage(reasoning="…", content="<|tool_call>…")
2. state.reasoning_ended = True; current_text is set to the post-<channel|> content
3. _extract_tool_calls_streaming() runs and replaces delta_message entirely
4. delta_message.reasoning is gone

Fix: Save delta_message.reasoning before calling _extract_tool_calls_streaming and restore it onto the result.

---

Bug 4 — multi-turn reasoning leak after a completed tool-response exchange (regression from Bug 1's fix)

File: vllm/reasoning/gemma4_reasoning_parser.py

Also closes #39885.

Bug 1's fix changed <|tool_response> handling from return False to continue. That is correct within a single turn, but on a second generation turn — after a completed <|tool_response>...<tool_response|> exchange sits in the prompt — the backward search now skips past <|tool_response> and finds the prior turn's <|tool_call>, so is_reasoning_end(prompt_token_ids) returns True from the very start of the new turn. With reasoning_ended pre-set, new-turn deltas go straight to the tool parser before any <|tool_call> appears, and the <|channel>thought… tokens leak as content.

Fix: Distinguish a bare <|tool_response> stop token (keep searching backward — Bug 1 behaviour) from one paired with a following <tool_response|> end marker (completed exchange → return False, model is in a fresh state and may generate new reasoning). Tracked via a saw_tool_response_end flag while scanning backward; <tool_response|> may be absent from the vocab, in which case the flag stays False and Bug 1 behaviour is preserved.

---

Bug 5 — empty reasoning_content emitted when the thinking block is empty

File: vllm/reasoning/gemma4_reasoning_parser.py

When the model emits <|channel>thought\n<channel|> with no reasoning inside (the thought\n role label is the whole block), prefix-stripping returned DeltaMessage(reasoning=""). The client received {"reasoning_content": ""} and some harnesses mis-rendered a stale thought\n<channel|> thinking box — notably when the response was only a tool call.

Fix: Return None (or forward post-channel content without a reasoning field) when the stripped reasoning is empty in the streaming path; map empty string to None via or None in the non-streaming path.

---

Why this is not duplicating existing PRs

• [Bugfix] Fix Gemma4 reasoning boundary around tool calls #42299 addresses the same is_reasoning_end root cause with a compatible approach. Our fix is narrower (one-line continue). The two fixes can coexist or be merged; we flag this explicitly so maintainers can choose.
• [Bugfix] Rewrite Gemma4 streaming tool parser #42237 (draft) and [Bugfix] Fix Gemma4 streaming tool calls with accumulated parser state #42300 rewrite the streaming tool parser entirely. Our tool-parser fix is a targeted change to the existing parser and is orthogonal to either rewrite.
• [Bugfix] Fix streaming tool call args blanked when entire call arrives in one delta #39615 (our earlier PR) fixed a narrower variant (args blanked, name already emitted). This PR fixes the case where neither name nor args are emitted at all.

Test plan

VLLM_USE_PRECOMPILED=1 .venv/bin/python -m pytest \
  tests/tool_parsers/test_gemma4_tool_parser.py \
  tests/reasoning/test_gemma4_reasoning_parser.py \
  tests/reasoning/test_gemma4_reasoning_with_tool_call.py \
  -q
# 92 passed

New tests:

• test_complete_tool_call_in_single_delta — exercises Bug 2
• test_gemma4_tool_response_does_not_block_reasoning_end — exercises Bug 1
• test_reasoning_then_tool_call_token_by_token — combined reasoning + tool call, token by token
• test_reasoning_then_tool_call_single_delta — exercises Bug 3 (was failing before the abstract_parser.py fix)
• test_reasoning_only_no_tool_call — reasoning with no tool call passes through cleanly
• test_reasoning_after_tool_response — exercises Bug 4 (multi-turn reasoning after a completed tool-response exchange)
• test_empty_thinking_block_tool_call_no_reasoning_leak — exercises Bug 5 (empty thinking block, token-by-token and single-delta)

AI assistance

Claude Code (claude-sonnet-4-6) was used to trace the token-level failure path and draft the fixes. Every changed line has been reviewed and tested end-to-end by the human submitter on a live Gemma4-26B-AWQ deployment with --stream-interval 20.

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[gemini-code-assist]

Code Review

This pull request addresses issues in the Gemma4 reasoning and tool parsers that occur when multiple tokens arrive in a single streaming delta due to batching. Key changes include updating the reasoning parser to correctly identify the end of reasoning by searching past tool response tokens and modifying the tool parser to initialize state and emit complete tool calls even when start and end tokens appear together. Review feedback points out that the current implementation still fails to handle cases where multiple distinct tool calls are contained within a single delta, which could lead to state synchronization issues or skipped tool calls.

[alexbi29]

Addressed all review feedback in f81af91. Requesting re-review from gemini-code-assist.

[gemini-code-assist]

Code Review

This pull request improves the Gemma4 reasoning and tool parsers to correctly handle cases where multiple tokens or tool calls are batched into a single streaming delta, often caused by stream-interval batching. Key changes include updating the reasoning parser to ensure tool response tokens do not mask preceding tool calls and modifying the tool parser to correctly initialize and emit multiple tool calls that arrive within the same chunk. I have no feedback to provide.

[gemini-code-assist]

Code Review

This pull request improves Gemma4 tool call parsing to handle scenarios where multiple tool calls or complete calls arrive within a single streaming delta. Key changes include updating the reasoning parser to correctly detect reasoning ends by skipping tool response tokens and modifying the tool parser to track and emit multiple tool calls batched in one chunk. A critical issue was identified in the tool parser's handling of mixed streaming scenarios, where an early return could lead to data loss for partially streamed calls when new complete calls are present in the same delta.

[alexbi29]

Addressed the mixed-streaming critical issue in dc7c1cf.

The problem: When a partially-streamed tool call finished in the same delta as new complete calls arrived, current_tool_name_sent was reset to False by Case 2 (incrementing current_tool_id for the new calls). This gated the function into the single-delta path, which skipped already-partially-streamed calls (their prev_tool_call_arr entry had a name) via continue and returned without emitting their remaining argument diff.

The fix: Replaced the two-branch logic (if not self.current_tool_name_sent / else) with a unified loop that iterates through every match up to current_tool_id and handles each according to its individual streaming state:

• If prev_tool_call_arr[idx] has no name → emit complete DeltaToolCall (name + full args)
• If prev_tool_call_arr[idx] has a name → emit remaining argument diff

Added test_streaming_mixed_partial_and_complete_in_one_delta that exercises this scenario end-to-end.

All 75 tests pass (46 tool parser + 29 reasoning parser). Requesting re-review from @gemini-code-assist.

[mergify]

Documentation preview: https://vllm--42875.org.readthedocs.build/en/42875/

[gemini-code-assist]

Code Review

This pull request updates the Gemma 4 tool parser and chat template to support multiple tool calls within a single streaming delta and refines reasoning token detection. Review feedback highlights several high-severity regressions, including the removal of support for multi-part system messages, the reasoning_content field, and the accidental deletion of critical unit tests for null values and floating-point streaming. Furthermore, the template now incorrectly filters standard JSON Schema keys from tool definitions, and the tool parser's global state management for concurrent tool calls needs correction to avoid skipping name emissions in subsequent deltas.

I am having trouble creating individual review comments. Click here to see my feedback.

vllm/tool_parsers/gemma4_tool_parser.py (738)

Setting self.current_tool_name_sent = True globally here is problematic when multiple tool calls are processed in a single delta. If a new tool call was started in the same delta (Case 2) but has not yet ended, it won't be in all_matches. By setting this flag to True now, the next delta's call to _handle_tool_call_middle for that new tool call will incorrectly assume the name has already been sent and skip emitting it. Since _handle_tool_call_end already correctly updates the state per-tool-call in self.prev_tool_call_arr[idx], this global flag update should be removed.

examples/tool_chat_template_gemma4.jinja (6)

Always filtering standard_keys in format_parameters is a regression. Tool parameters are allowed to have names like type or description according to the JSON Schema spec. The previous implementation correctly used a filter_keys parameter to only apply this filtering when recursing on a "flat" object definition (where the metadata keys are mixed with property definitions). By removing that toggle, any tool parameter named after a standard key will be silently omitted from the model's tool definition.

examples/tool_chat_template_gemma4.jinja (225-226)

This change removes support for the reasoning_content field in assistant messages. vLLM's OpenAI-compatible API uses reasoning_content for thinking text. Removing this check is a regression that will prevent reasoning from being rendered in the chat history for models that use that field name.

    {%- set thinking_text = message.get('reasoning') or message.get('reasoning_content') -%}
    {%- if thinking_text and loop.index0 > ns_turn.last_user_idx and message.get('tool_calls') -%}
        {{- '<|channel>thought\n' + thinking_text + '\n<channel|>'}}

examples/tool_chat_template_gemma4.jinja (180)

This change removes support for multi-part content (list of text parts) in the system/developer message. This is a regression from the previous implementation which correctly handled both string and sequence content types.

        {%- if messages[0]['content'] is string -%}
            {{- messages[0]['content'] | trim -}}
        {%- elif messages[0]['content'] is sequence -%}
            {%- for item in messages[0]['content'] -%}
                {{- item['text'] | trim + ' '-}}
            {%- endfor -%}
        {%- endif -%}

tests/tool_parsers/test_gemma4_tool_parser.py (88-94)

This PR accidentally deletes several important unit tests, including support for null values in tool arguments. These tests ensure the parser correctly handles edge cases and should be restored.

tests/tool_parsers/test_gemma4_tool_parser.py (138-161)

This PR deletes a critical regression test for issue #42047 regarding trailing dots in floating point numbers during streaming. Deleting this test risks re-introducing streaming diff corruption bugs.

[alexbi29]

Addressed all recent review feedback in three fixups:

1. Mixed-streaming data loss (critical issue from last review):
When a partially-streamed tool call finished in the same delta as new complete calls arrived, current_tool_name_sent was reset to False by Case 2 (incrementing current_tool_id for the new calls). This gated _handle_tool_call_end into the single-delta path, which skipped already-partially-streamed calls (their prev_tool_call_arr entry had a name) via continue and returned without emitting the arg diff.

Fix: Replaced the two-branch logic with a unified loop that checks each match's individual streaming state (prev_tool_call_arr[idx]). (commit 79631cfc)

2. Global current_tool_name_sent flag regression:
Setting self.current_tool_name_sent = True at end of _handle_tool_call_end would suppress name emission for any new call started by Case 2 that hadn't ended yet. Removed the flag — per-index tracking is sufficient. (commit 2a72586d)

3. Reverted accidental chat template + test deletions:
The branch had picked up commit 5ad4f2f2 which inadvertently dropped filter_keys parameter, reasoning_content support, and multi-part system messages from the chat template, and deleted several unit tests including the null-value and trailing-dot-float regression tests. These are now reverted. (commit b43eec94)

Tests: 84/84 passing (54 tool parser + 30 reasoning parser).

@\gemini-code-assist please re-review.

[gemini-code-assist]

Code Review

This pull request improves the Gemma4 tool parser and reasoning parser to correctly handle cases where multiple tool calls or reasoning-to-tool transitions occur within a single streaming delta. Key changes include updating the reasoning parser to continue searching for tool call tokens even when response tokens are present, and refactoring the tool parser to iterate through and emit all tool calls that start or end within the same chunk. Feedback identifies a high-severity issue where model-generated text surrounding tool call tokens might be silently dropped in the current implementation, leading to potential data loss during streaming.

[gemini-code-assist]

Code Review

This pull request fixes issues with Gemma4 tool parsing and reasoning end detection when multiple tokens or entire tool calls arrive in a single streaming delta. Key changes include updating is_reasoning_end to continue searching past tool response tokens and refactoring the tool parser to handle multiple tool calls within one delta. New tests cover single-delta complete calls, multiple calls, and mixed streaming scenarios. I have no feedback to provide.

[alexbi29]

Addressed the leading/trailing content loss issue flagged in the last review.

Problem: Model-generated text that shares a streaming delta with tool call markers was silently dropped in two scenarios:

1. Trailing content after <tool_call|> (e.g. }<tool_call|> Some text)
2. Leading content before <|tool_call> (e.g. Answer: <|tool_call>call:func{...})

Fix: At the Case 3 level in _extract_streaming, extract both leading content (before first <|tool_call>) and trailing content (after last <tool_call|>) from the buffered delta_text and merge them into the result DeltaMessage alongside the tool calls. Using the buffered delta_text (not current_text) is critical to avoid emitting partial tokens that _buffer_delta_text correctly held back (e.g. a stray < that belongs to the next chunk). Also added the same leading-content rescue at the Case 4 level when _handle_tool_call_middle returns None because the tool call header is not yet parseable.

Tested live on gemma4-26b with --stream-interval 20 — content preserved alongside tool calls, valid JSON arguments.

Test suite: 84/84 passing (54 tool parser + 30 reasoning parser).

@\gemini-code-assist please re-review.

[gemini-code-assist]

Code Review

This pull request enhances the Gemma4 reasoning and tool parsers to handle cases where multiple tool calls or a complete tool call arrive in a single streaming delta. The reasoning parser now correctly identifies the end of reasoning by searching past tool response tokens, and the tool parser has been refactored to process multiple tool call starts and ends within the same chunk while capturing surrounding content. A review comment pointed out a critical bug where the parser's internal state is not reset between requests, potentially leading to state leakage in multi-request environments.

[alexbi29]

Addressed the state-leakage issue.

Problem: _reset_streaming_state() was only called in __init__, but the parser instance is reused across all streaming requests. After request 1 processed tool calls, stale state (current_tool_id, prev_tool_call_arr, streamed_args_for_tool) leaked into request 2, causing tool calls to start at index=1 instead of index=0 and accumulating stale entries.

Fix: Call _reset_streaming_state() in extract_tool_calls_streaming when previous_text == "" (the first delta of each new request). Also added buffered_delta_text reset to _reset_streaming_state() for completeness.

Reproduction: Before the fix, two consecutive single-tool-call requests would show current_tool_id=0 → 1 (should be 0 → 0) and prev_tool_call_arr growing from 1 to 2 entries (should stay at 1). After the fix, the second request starts clean at index=0.

Tests: 84/84 passing. State-leak reproduction script confirms clean state after fix.

@\gemini-code-assist all feedback addressed, please re-review.

[gemini-code-assist]

Code Review

This pull request enhances the Gemma4 reasoning and tool parsers to handle batched streaming tokens, ensuring that complete or multiple tool calls arriving in a single delta are processed correctly. It updates the reasoning parser's logic for detecting the end of reasoning and fixes state leakage in the tool parser between requests. Review feedback identifies potential issues where raw tool call tags could leak into the message content and where leading text might be lost during streaming, providing code suggestions to handle these edge cases.

[alexbi29]

Addressed the two remaining issues from the latest review:

Issue A — Raw tool call tags leaking into content:
Leading and trailing content extracted from delta_text in Case 3 now have tool call tags stripped via .replace(). Also added handling for the first_start == -1 case (text before an end token with no preceding start token).

Issue B — Leading content lost in Case 4:
The leading-content rescue was gated on result is None, so it didn't fire when _handle_tool_call_middle returned a name or arg diff. Fixed by always checking for leading content regardless of result value.

Reproduction: Both scenarios were reproduced before the fix (confirmed via standalone scripts) and confirmed resolved after.

Tests: 84/84 passing.

@\gemini-code-assist all feedback addressed, please re-review.

[gemini-code-assist]

Code Review

This pull request enhances the Gemma4 reasoning and tool parsers to correctly handle batched streaming deltas where multiple tool calls or reasoning end tokens may arrive simultaneously. Key changes include updating the reasoning parser to continue searching for tool calls past response tokens and refactoring the tool parser to support multiple tool calls per delta and extract surrounding text. Review feedback identifies a critical race condition where resetting streaming state on a shared parser instance could corrupt concurrent requests, as well as a logic error in text extraction that may cause duplicated or missing content when multiple tool calls appear in the same chunk.

[alexbi29]

Addressed both issues from the latest review:

1. Duplicated/missing inter-call text (fixed):
When delta_text had an end token before a start token
(<tool_call|> text <|tool_call>...), the inter-call text was captured
by BOTH leading and trailing extraction, producing duplicate content
(e.g. " and then and then "). Fixed by clipping trailing_start to
first_start + len(start_token) when the last end token falls before
the first start token.

2. Race condition on state reset (not a practical concern):
The previous_text == "" check is safe in vLLM architecture -
the parser instance is reused across sequential requests, not concurrent
ones. The serving loop processes one request at a time.

Tests: 84/84 passing.

@gemini-code-assist please re-review.

[gemini-code-assist]

Code Review

This pull request enhances the Gemma4 reasoning and tool parsers to handle batched streaming deltas where multiple tool calls or a mix of reasoning and tool calls arrive simultaneously. The changes include updating the reasoning parser to correctly identify the end of reasoning when followed by tool responses, refactoring the tool parser to support multiple tool calls per delta, and ensuring state is reset between requests. Feedback was provided regarding a logic error in the content extraction logic that could cause raw tool call markers to leak into the output content when multiple markers appear in a specific sequence.

[alexbi29]

Addressed the latest feedback.

Issue: When delta_text had an end token followed by a new incomplete start token (e.g. <tool_call|> text <|tool_call>call:func2{...), my previous fix clipped trailing_start past the start token, causing the raw tool call body (call:func2{...}) to leak into content.

Fix: When trailing_start < first_start, set after = "". The inter-call text is already captured as leading content; there is no valid trailing content in this case.

Reproduction: Confirmed the leak before fix (content contained call:func2{arg2:...}), clean after fix (content=' then ' only).

Tests: 84/84 passing.

@gemini-code-assist please re-review.

[gemini-code-assist]

Code Review

This pull request improves the Gemma4 reasoning and tool parsers to correctly handle scenarios where multiple tool calls or tokens are batched into a single streaming delta, often caused by stream-interval batching. Key changes include updating the reasoning parser to continue searching for tool calls past tool response tokens and refactoring the tool parser to support multiple tool calls per delta and better content extraction. Review feedback highlights potential issues with the content extraction logic, specifically regarding content leakage of raw argument fragments and the loss of intermediate text between multiple tool calls in the same delta.

[alexbi29]

Squashed the branch into a single commit (a48c669d) on top of latest main and addressed the last two issues from gemini-code-assist in the same pass. PR description still describes the full scope; this comment summarizes the final state.

What was fixed

Bug 1 — Reasoning parser missed is_reasoning_end

vllm/reasoning/gemma4_reasoning_parser.py

When <|tool_response> appeared in the same delta as <|tool_call> (common with --stream-interval batching), the reverse search through token IDs hit <|tool_response> first and returned False, so state.reasoning_ended was never set. The tool-call phase never activated, and the raw <|tool_call>…<tool_call|> text leaked downstream as content.

Fix: in the reverse walk, treat <|tool_response> as continue (it is a generation stop token, always the last token, never followed by new model output in the same streaming delta), so the search reaches the preceding <|tool_call> and correctly returns True. The new_turn_token_id guard for multi-turn re-entry is preserved.

Bug 2 — Tool parser dropped single-delta tool calls

vllm/tool_parsers/gemma4_tool_parser.py

Once the tool-call phase was entered, extract_tool_calls_streaming received the entire <|tool_call>call:fn{…}<tool_call|> text in one delta. Multiple coupled fixes were required:

1. Case 2 previously required start_count > end_count, which was false when start and end arrived in the same delta. State was never initialised. Now Case 2 initialises tool state on any new start token, looping N times when N>1 tool calls arrive in one delta.

2. _handle_tool_call_end now iterates over every match up to current_tool_id and dispatches per-call based on prev_tool_call_arr[idx]: emit name + full args for calls whose name was never streamed, emit the remaining argument diff for partially-streamed calls. This is what makes auto_tools_called true in serving.py so finish_reason becomes "tool_calls" instead of "stop".

3. _extract_content_outside_tool_calls — new helper that walks delta_text and collects text spans outside any <|tool_call>…<tool_call|> pair, with started_inside = prev_start_count > prev_end_count so it knows whether the delta begins inside an active tool call. Replaces the previous brittle leading/trailing slicing in Case 3 and Case 4 and resolves the two remaining issues from the last review:

   • Content leakage when started inside a call: bytes before the first end token belong to the ongoing call's arguments, not content. The walker correctly skips them, so raw arg fragments like } or <|"|> no longer leak.
   • Lost inter-call text: plain text between two completed calls in one delta (<|tool_call>…<tool_call|> X <|tool_call>…<tool_call|>) is now captured. End-then-start cases (<tool_call|>X<|tool_call>…) no longer duplicate or drop X.
     The walker never emits tool call markers (no .replace() games — it skips past them by construction).

4. Per-request state reset: extract_tool_calls_streaming calls _reset_streaming_state() when previous_text == "" so current_tool_id, prev_tool_call_arr, streamed_args_for_tool, and buffered_delta_text do not leak across sequential requests on the reused parser instance.

Verification

Unit tests: 87/87 pass (57 tool parser + 30 reasoning parser).

Three new tests directly cover the final-review scenarios:

• test_streaming_inter_call_text_preserved_in_single_delta — text between two tool calls in one delta is captured.
• test_streaming_no_arg_fragment_leak_when_started_inside — delta starting mid-call does not leak arg fragments as content.
• test_streaming_end_then_start_no_duplication — end-then-start in one delta is captured exactly once.

Plus the earlier additions: test_complete_tool_call_in_single_delta, test_multiple_tool_calls_in_single_delta, test_streaming_mixed_partial_and_complete_in_one_delta, test_gemma4_tool_response_does_not_block_reasoning_end.

Live end-to-end: ran a streaming client against a live gemma4-26b deployment with --stream-interval 20 (the exact configuration that originally reproduced the bug). Three scenarios verified: single tool call (get_weather), two tool calls in one response (read_file ×2), and a content-only no-tool-call reply. In every case finish_reason is correct, arguments parse as JSON, and content contains no raw markers or argument fragments.

@gemini-code-assist please re-review.

[gemini-code-assist]

Code Review

This pull request enhances the Gemma 4 reasoning and tool parsers to robustly handle batched streaming deltas, particularly when multiple tool calls or complete calls arrive in a single chunk. Key changes include updating the reasoning parser to correctly identify the end of reasoning when followed by tool responses, and refactoring the tool parser to track and emit multiple tool calls and inter-call text within the same delta. Extensive tests were added to cover various streaming edge cases, such as mixed partial and complete calls and preventing argument fragment leaks. I have no feedback to provide.

[alexbi29]

@bbrowning this PR should be gtg.
Tested on both gemma4-26b and gemma4-31b, customer apps, hermes agent and pi.dev.

[alexbi29]

@bbrowning would you be able to review this? It fixes a bug in DelegatingParser.parse_delta (Bug 3) where reasoning content is silently dropped when the reasoning block and tool call land in the same streaming delta (--stream-interval 20). Closes #39885.

[alexbi29]

Update: Multi-turn reasoning leak fix added

A second bug has been identified and fixed in this PR: multi-turn reasoning leak after a tool response (also related to #39885).

Root cause

After a completed tool call + tool response exchange, is_reasoning_end(prompt_token_ids) incorrectly returned True because:

1. When searching backward through prompt_token_ids, the code encountered <|tool_response> (start token) and used continue to skip past it
2. This led to finding the prior turn's <|tool_call> token and returning True
3. With reasoning_ended=True set from the very start of the new generation, all deltas went directly to the tool parser
4. The tool parser saw <|channel>thought... tokens and emitted them as content — raw thinking tokens leaked into the response

Fix

is_reasoning_end now tracks whether a <tool_response|> end marker was passed while searching backward. When <|tool_response> is encountered:

• With a preceding <tool_response|> (prompt context: completed exchange) → return False (fresh start, new reasoning may follow)
• Without <tool_response|> (delta context: bare stop token appended after model's tool call) → keep searching backward (original behaviour)

Tested

New test test_reasoning_after_tool_response in tests/reasoning/test_gemma4_reasoning_with_tool_call.py — passes, and the pre-existing test_gemma4_tool_response_does_not_block_reasoning_end continues to pass.

@bbrowning

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @alexbi29.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork