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report.md

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+# Gemma-4 tool calling: constrained (xgrammar) vs unconstrained
+
+- model: `google/gemma-4-E2B-it` via HF transformers
+- constraint: `xgr.get_model_structural_tag("gemma_4", tools=..., tool_choice="required")` compiled and applied with `xgr.contrib.hf.LogitsProcessor`
+- 4 samples per scenario per mode; identical sampling settings for both modes (per-scenario values below)
+- outputs validated with a pure-Python port of sglang's `Gemma4Detector` parser plus `jsonschema`
+
+## Results (passing samples / total)
+
+### A. complex-schema
+
+temperature=0.9, top_p=0.95, max_new_tokens=384, reasoning=False
+
+| metric | constrained | unconstrained |
+|---|---|---|
+| well_formed | 4/4 ✅ | 4/4 ✅ |
+| valid_name | 4/4 ✅ | 4/4 ✅ |
+| schema_valid | 4/4 ✅ | 4/4 ✅ |
+| stops_at_boundary | 4/4 ✅ | 0/4 ❌ |
+
+### B. multiturn-thinking
+
+temperature=0.9, top_p=0.95, max_new_tokens=384, reasoning=True
+
+| metric | constrained | unconstrained |
+|---|---|---|
+| well_formed | 4/4 ✅ | 4/4 ✅ |
+| valid_name | 4/4 ✅ | 4/4 ✅ |
+| schema_valid | 4/4 ✅ | 4/4 ✅ |
+| stops_at_boundary | 4/4 ✅ | 0/4 ❌ |
+| thought_ok | 4/4 ✅ | 0/4 ❌ |
+
+### C. adversarial-payload
+
+temperature=1.5, top_p=1.0, max_new_tokens=640, reasoning=False
+
+| metric | constrained | unconstrained |
+|---|---|---|
+| well_formed | 4/4 ✅ | 4/4 ✅ |
+| valid_name | 4/4 ✅ | 4/4 ✅ |
+| schema_valid | 4/4 ✅ | 4/4 ✅ |
+| stops_at_boundary | 4/4 ✅ | 0/4 ❌ |
+
+## Metric definitions
+
+- `well_formed` — every tool call block is complete and parseable (sglang parser port)
+- `valid_name` — every called tool exists
+- `schema_valid` — parsed arguments validate against the tool's JSON schema
+- `stops_at_boundary` — generation did not run past <tool_call|> into <|tool_response>
+- `thought_ok` — <|channel>thought opened and closed before the first tool call
+
+## Failure examples
+
+**A. complex-schema / unconstrained #0** — failed `stops_at_boundary`: ran past <tool_call|> into <|tool_response> after the call
+
+```
+<|tool_call>call:create_calendar_event{attendees:[{email:<|"|>alice.kim@example.com<|"|>,name:<|"|>Alice Kim<|"|>},{email:<|"|>bob.lee@example.com<|"|>,name:<|"|>Bob Lee<|"|>},{email:<|"|>chris.park@example.com<|"|>,name:<|"|>Chris Park<|"|>}],duration_minutes:90,location:{floor:7,room:<|"|>Jupiter<|"|>},priority:<|"|>high<|"|>,send_invites:true,start:<|"|>2026-07-10T14:00:00+09:00<|"|>,title:<|"|>Q3 Roadmap Review ("final" draft)<|"|>}<tool_call|><|tool_response>
+```
+
+**A. complex-schema / unconstrained #1** — failed `stops_at_boundary`: ran past <tool_call|> into <|tool_response> after the call
+
+```
+<|tool_call>call:create_calendar_event{attendees:[{email:<|"|>alice.kim@example.com<|"|>,name:<|"|>Alice Kim<|"|>},{email:<|"|>bob.lee@example.com<|"|>,name:<|"|>Bob Lee<|"|>},{email:<|"|>chris.park@example.com<|"|>,name:<|"|>Chris Park<|"|>}],duration_minutes:90,location:{floor:7,room:<|"|>Jupiter<|"|>},priority:<|"|>high<|"|>,send_invites:true,start:<|"|>2026-07-10T14:00:00+09:00<|"|>,title:<|"|>Q3 Roadmap Review ("final" draft)<|"|>}<tool_call|><|tool_response>
+```
+
+**A. complex-schema / unconstrained #2** — failed `stops_at_boundary`: ran past <tool_call|> into <|tool_response> after the call
+
+```
+<|tool_call>call:create_calendar_event{attendees:[{email:<|"|>alice.kim@example.com<|"|>,name:<|"|>Alice Kim<|"|>},{email:<|"|>bob.lee@example.com<|"|>,name:<|"|>Bob Lee<|"|>},{email:<|"|>chris.park@example.com<|"|>,name:<|"|>Chris Park<|"|>}],duration_minutes:90,location:{floor:7,room:<|"|>Jupiter<|"|>},priority:<|"|>high<|"|>,send_invites:true,start:<|"|>2026-07-10T14:00:00+09:00<|"|>,title:<|"|>Q3 Roadmap Review ("final" draft)<|"|>}<tool_call|><|tool_response>
+```
+
+**A. complex-schema / unconstrained #3** — failed `stops_at_boundary`: ran past <tool_call|> into <|tool_response> after the call
+
+```
+<|tool_call>call:create_calendar_event{attendees:[{email:<|"|>alice.kim@example.com<|"|>,name:<|"|>Alice Kim<|"|>},{email:<|"|>bob.lee@example.com<|"|>,name:<|"|>Bob Lee<|"|>},{email:<|"|>chris.park@example.com<|"|>,name:<|"|>Chris Park<|"|>}],duration_minutes:90,location:{floor:7,room:<|"|>Jupiter<|"|>},priority:<|"|>high<|"|>,send_invites:true,start:<|"|>2026-07-10T14:00:00+09:00<|"|>,title:<|"|>Q3 Roadmap Review ("final" draft)<|"|>}<tool_call|><|tool_response>
+```
+
+**B. multiturn-thinking / unconstrained #0** — failed `stops_at_boundary`, `thought_ok`: ran past <tool_call|> into <|tool_response> after the call; skipped or never closed the <|channel>thought section
+
+```
+<|tool_call>call:convert_temperature{from_unit:<|"|>celsius<|"|>,to_unit:<|"|>fahrenheit<|"|>,value:3}<tool_call|><|tool_response>
+```
+
+**B. multiturn-thinking / unconstrained #1** — failed `stops_at_boundary`, `thought_ok`: ran past <tool_call|> into <|tool_response> after the call; skipped or never closed the <|channel>thought section
+
+```
+<|tool_call>call:convert_temperature{from_unit:<|"|>celsius<|"|>,to_unit:<|"|>fahrenheit<|"|>,value:3}<tool_call|><|tool_response>
+```
+
+**B. multiturn-thinking / unconstrained #2** — failed `stops_at_boundary`, `thought_ok`: ran past <tool_call|> into <|tool_response> after the call; skipped or never closed the <|channel>thought section
+
+```
+<|tool_call>call:convert_temperature{from_unit:<|"|>celsius<|"|>,to_unit:<|"|>fahrenheit<|"|>,value:3}<tool_call|><|tool_response>
+```
+
+**B. multiturn-thinking / unconstrained #3** — failed `stops_at_boundary`, `thought_ok`: ran past <tool_call|> into <|tool_response> after the call; skipped or never closed the <|channel>thought section
+
+```
+<|tool_call>call:convert_temperature{from_unit:<|"|>celsius<|"|>,to_unit:<|"|>fahrenheit<|"|>,value:3}<tool_call|><|tool_response>
+```
+
+**C. adversarial-payload / unconstrained #0** — failed `stops_at_boundary`: ran past <tool_call|> into <|tool_response> after the call
+
+```
+<|tool_call>call:create_ticket{affected:{regions:[<|"|>ap-northeast-2<|"|>,<|"|>us-east-1<|"|>],service:<|"|>payments<|"|>,version:<|"|>2.14.1<|"|>},body:<|"|>Deployed config: {"retry": {"max": 3, "backoff_ms": [100, 200], "jitter": true}}
+Error line: TypeError: cannot destructure {id: undefined} at applyRetry (retry.js:42).<|"|>,cc_emails:[<|"|>dev-alerts@example.com<|"|>],estimated_minutes:45,labels:[<|"|>regression<|"|>,<|"|>backend<|"|>],severity:<|"|>blocker<|"|>,title:<|"|>Payments retry storm after config rollout<|"|>,urgent_escalation:true}<tool_call|><|tool_response>
+```
+
+**C. adversarial-payload / unconstrained #1** — failed `stops_at_boundary`: ran past <tool_call|> into <|tool_response> after the call
+
+```
+<|tool_call>call:create_ticket{affected:{regions:[<|"|>ap-northeast-2<|"|>,<|"|>us-east-1<|"|>],service:<|"|>payments<|"|>,version:<|"|>2.14.1<|"|>},body:<|"|>Deployed config: {"retry": {"max": 3, "backoff_ms": [100, 200], "jitter": true}}
+Error line: TypeError: cannot destructure {id: undefined} at applyRetry (retry.js:42).<|"|>,cc_emails:[<|"|>dev-alerts@example.com<|"|>],estimated_minutes:45,labels:[<|"|>bug<|"|>,<|"|>regression<|"|>,<|"|>backend<|"|>],severity:<|"|>blocker<|"|>,title:<|"|>Payments retry storm after config rollout<|"|>,urgent_escalation:true}<tool_call|><|tool_response>
+```
+
+**C. adversarial-payload / unconstrained #2** — failed `stops_at_boundary`: ran past <tool_call|> into <|tool_response> after the call
+
+```
+<|tool_call>call:create_ticket{affected:{regions:[<|"|>ap-northeast-2<|"|>,<|"|>us-east-1<|"|>],service:<|"|>payments<|"|>,version:<|"|>2.14.1<|"|>},body:<|"|>Deployed config: {"retry": {"max": 3, "backoff_ms": [100, 200], "jitter": true}}
+Error line: TypeError: cannot destructure {id: undefined} at applyRetry (retry.js:42)<|"|>,cc_emails:[<|"|>dev-alerts@example.com<|"|>],estimated_minutes:45,labels:[<|"|>bug<|"|>,<|"|>regression<|"|>,<|"|>backend<|"|>],severity:<|"|>blocker<|"|>,title:<|"|>Payments retry storm after config rollout<|"|>,urgent_escalation:true}<tool_call|><|tool_response>
+```
+
+**C. adversarial-payload / unconstrained #3** — failed `stops_at_boundary`: ran past <tool_call|> into <|tool_response> after the call
+
+```
+<|tool_call>call:create_ticket{affected:{regions:[<|"|>ap-northeast-2<|"|>,<|"|>us-east-1<|"|>],service:<|"|>payments<|"|>,version:<|"|>2.14.1<|"|>},body:<|"|>Deployed config: {"retry": {"max": 3, "backoff_ms": [100, 200], "jitter": true}}
+Error line: TypeError: cannot destructure {id: undefined} at applyRetry (retry.js:42).<|"|>,cc_emails:[<|"|>dev-alerts@example.com<|"|>],estimated_minutes:45,labels:[<|"|>bug<|"|>,<|"|>regression<|"|>,<|"|>backend<|"|>],severity:<|"|>blocker<|"|>,title:<|"|>Payments retry storm after config rollout<|"|>,urgent_escalation:true}<tool_call|><|tool_response>
+```