[leehack]

Summary

• Maintainer decisions on #1542: Seed-OSS tool-call start matches llama.cpp (cd959bae9) ("Match llama.cpp (Recommended)"); an unknown tool and a missing required argument stay lenient and documented ("Keep lenient, document").
• Behavior change (Seed-OSS only): calls start at the first <seed:tool_call> followed by \n anywhere in the reply, as llama.cpp does; text before it, including a <seed:tool_call> not followed by \n, is content. The tool-call grammar (auto and ToolChoice.required) now requires "<seed:tool_call>\n", matching llama.cpp's "<seed:tool_call>\n" space, and the compact lazy trigger <seed:tool_call><function= is gone.
• Implementation: XmlToolCallFormat.seedOss.scopeStart is now '<seed:tool_call>\n' (one Seed-only hunk in the shared xml_tool_call_format.dart; no overlap with #1885's hunks), so the parse, stream gate and grammar share it. The handler's first-tag gate is removed.
• Docs: template-engine-internals.md, fixture notes, both changelog bullets.

Refs #1542, #1531.

Production-readiness scope

• User-facing scope: <seed:tool_call><function=... (or a space/tab/CRLF after the tag) is content, not a call; a line-broken scope after such text or a compact scope is now found (708a852 returned no call; main returned the compact one too). A later scope without \n after valid calls stays content after them (main returned it as a call; llama.cpp fails the reply). Unknown tools and missing arguments: rejected for ToolDefinition.fromJsonSchema tools, returned as calls otherwise; documented.
• Supported platforms/paths: All (shared Dart template parsing and GBNF).
• Unsupported or intentionally unavailable paths: None.
• Out of scope / follow-ups: Pre-existing divergences left as on main: content before calls is trimmed (llama.cpp keeps a trailing \n); a first line-broken scope holding no valid call keeps the reply as content where llama.cpp errors; two calls with parallelToolCalls: false are both returned where llama.cpp errors.

Completeness checklist

• Declared scope is fully implemented.
• Unsupported combinations: N/A.
• Docs and changelog updated.
• Regression coverage, failing first at 708a852: multi-scope parse, scope tag inside a thought, later compact scope, end-of-output hold in the stream, trigger list, compiled-grammar rejection of compact/space scopes (auto, parallel and required). Mutation pass: 7/7 killed (table below).
• Validation registry: N/A, no capability change.
• Security/privacy review: nothing sensitive.
• Follow-ups: the pre-existing divergences above, under Reasoning parity follow-ups from #1524/#1525 audit: mutants X2/X7, Ling <think> in args, partial-tag drop #1531.

PR type guidance

• Bugfix PR: re-audit of 708a852 found (B1) the grammar and lazy trigger still admitted <seed:tool_call><function= that the parse discarded, so ToolChoice.required could end with 0 calls, and (B2) calls were decided by the first tag instead of the first line-broken scope. Root cause for both: Seed's scope start lacked the \n llama.cpp requires.

Test Plan

• dart run tool/prepare_workspace.dart (tree clean after)
• dart format --output=none --set-exit-if-changed .
• dart analyze: no issues
• dart run tool/testing/check_platform_boundaries.dart
• dart test -p vm -j 1 --exclude-tags local-only (macOS, isolated TMPDIR): 11964 passed; 6 failures only in windows_registry_qualification_test.dart (pwsh not installed on this host, unrelated)
• GBNF e2e specialized_tool_grammar_validation_e2e_test.dart --run-skipped with llama.cpp cd959bae9 test-gbnf-validator: 79 passed
• dart test -p chrome: N/A, parsing is platform-independent; CI runs it
• coverage-lib: left to CI on main
• ./tool/docs/build_site.sh --port 61136: no broken internal links

Matrix Evidence

Matrix row	Scope covered	Platform / model / backend	Result	Evidence / notes
structured-output-adversarial	Seed-OSS parse, stream, auto/required/parallel grammar acceptance and rejection, upstream parity	VM, llama.cpp cd959bae9 oracle and GBNF validator	PASS	Oracle below; GBNF e2e 79/79
Upstream parity	Auditor's 24-case harness × thinking × parallel × whole/bytewise (192)	VM	76 strict mismatches, 0 regressions	llamadart-evidence/pr-1886/oracle/fix-new/
high-risk-exact-head-independent-qa	Exact head	—	Pending	Re-audit requested

Oracle (strict / categorised) vs llama.cpp cd959bae9:

Build	Match	Different calls	llama.cpp errors	Content trim only	Reasoning with thinking off	Other content
main 77b01da	52	88	28	8	8	8
708a852	116	16	28	8	16	8
this head	116	0	28	24	16	8

No case matching at main or 708a852 mismatches now. The 16 "different calls" at 708a852 (compact-then-valid, mention-then-valid) now return llama.cpp's calls, differing only by the existing content trim. ToolChoice.required grammar: compact and space-after-tag scopes are now invalid in the compiled grammar (both thinking modes); the line-broken scope is valid.

Mutants (oracle/fix-new/mutants.log):

Mutant	Result
Seed scope start without \n	Killed (7 tests incl. GBNF e2e)
Compact lazy trigger restored	Killed
Trigger without \n	Killed
708a852 first-tag gate restored	Killed
First-tag gate on raw output (M6)	Killed
Last scope instead of first (M5)	Killed (52)
Later compact scope accepted	Killed

Review Notes

• Independent review status: audit at 154fed33 failed on doc accuracy; re-audit at 708a852 failed (B1, B2); this head addresses both plus the non-blocking end-of-output, M6 and later-scope items. Re-audit pending.
• CI status / head SHA: green (CI run; 32 pass, 9 skipped) / 67d1651

High-risk regression review

• Classification: high-risk (structuredOutput)
• Implementation task: this PR
• Independent blocking QA task: pending re-audit
• Exact head / current base: 67d1651 / 77b01da
• Production-branch deletion, bypass, or miswire proof: mutants above
• Affected-family real-model/artifact evidence: llama.cpp cd959bae9 oracle and GBNF validator on the vendored Seed-OSS template; no model weights
• Explicit unavailable-family or other N/A evidence: Seed-OSS weights not used; parser/grammar-level evidence only
• Known PR-caused P1 regressions: 0
• Unresolved review threads: 0

[leehack]

Landed on main via batch integration PR #1895 (rebase merge, main ba4e0e1b; tree identical to the audited integration head 5ffd1224).

[github-actions]

Chat app preview removed for leehack/llamadart-chat-pr-1886.