[slin1237]

What

Stacked on #2877 (base feat/symphony-grammar): the second syntax the gateway hand-writes a structural tag for, Kimi K3's XTML, now derives from the table, inside crates/symphony/ only.

• Regions, not emissions. Format::grammar read its markers off the first row between two kinds of state; a table with two wrapper states (Kimi K3's message, the turn itself, and tools, the block) breaks that. The derivation now reads the table as regions: a region's close is the terminal of the row from its state back to a state it is entered from, and its opener the terminal of that state's row in; the terminal every state has a row for back to the turn's own state is the end of the turn (<|close|>message<|sep|>), which ends whatever is open and closes no region. The call, the block (the wrapper state with a row into the arguments state) and the thought all take their markers that way, whatever the order of the rows (a test rebuilds Kimi K3's table from its rows in reverse). Format::states() (crate-level) gives the count the end-of-turn rule needs.
• Kimi K3's tag (grammar/xtml.rs): one way into the block per state it is entered from, in the order of the states (the turn itself, the thought, the answer), from a region with a close of its own, that close and then the row into the block from the state the close returns to, and from the turn's own state or a state with no close, its own row; the same way in once; each closed by the block's close, with each way's first text as its trigger; inside, one or more calls (plus of an or over the named tools), each the call's opener with the escaped name and index="[1-9][0-9]*", the arguments, and the call's close. The tag takes no reasoning prefix: the model closes whatever the prompt left open on its way in, so reasoning_open changes nothing for it.
• The argument shapes are the old Kimi K3 parser's, ported to the Grammar tree (rule 27: the file's authors and the co-authors its history names are co-authors of the squash): one tag per property in the schema's order, optional unless required; a string as any text up to a marker, a string enum as one of its values, integer/number as number with the property's schema, object and array likewise with the tool's $defs/definitions attached so a local $ref still resolves, boolean as JSON, null as the word; any type and any value for an untyped property or a pointer at nothing; any arguments for a schema without properties. & and " are escaped in attributes as the template writes them.

Parity

Old builder	Derived from	Pinned
KimiK3Parser::build_structural_tag	formats::kimi_k3()	triggers, the three begins in order, one end, identical content per way in, plus/or, at_least_one both ways
build_call_format	the call's markers from the table	the five elements literally
build_args_format, classify_arg, escape_attr, the permissive shapes	the tool's schema	string, number, enum, boolean, array, object, null, $ref with definitions attached, dangling $ref, untyped, no properties, escaping

The one difference from the old builder is the same as GLM's and DSML's: no named tool gives None here, where the old builder wrote a call with any name. The GLM, DSML and JSON-family tags from #2877 are unchanged by the region rules (their tests still pass as written), and the row-order test still swaps DeepSeek V4.1's exits.

Gates

By exit code (.claude/symphony/gates.sh, base feat/symphony-grammar): fmt, clippy -D warnings, test (328 lib, 10 fixture, 7 contract, 5 README), doc, width, codespell, all 0.

Not in this PR

• The remaining syntaxes still answer None: the tagged syntax (Qwen 3.5 and later, Seed-OSS), Ling's and Hy4's keyed spellings, MiniMax M3's XML, the pythonic tables, xLAM's list.
• The gateway wiring and the Constrained adapter (feat(symphony): the constrained format for a forced or required tool choice #2806); acceptance of the derived tags by xgrammar itself (bellwether, once the recorder has a constrained run).

Merge

After #2877, rebased onto main. Squash under rule 25 (rule 18: no new CallSyntax; Format gains a crate-level accessor only; the maintainer merges). Subject: the PR title plus (#<n>). Body:

Signed-off-by: Simo Lin <25425177+slin1237@users.noreply.github.com>
Co-authored-by: Chang Su <8605658+CatherineSue@users.noreply.github.com>
Co-authored-by: Keyang Ru <rukeyang@gmail.com>
Co-authored-by: key4ng <key4ng@users.noreply.github.com>
Co-authored-by: Chen Hongtao <56470055+chenht2022@users.noreply.github.com>
Co-authored-by: LightSeek Foundation <243258330+lightseek-bot@users.noreply.github.com>

[coderabbitai]

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• crates/symphony/src/grammar.rs
• crates/symphony/src/grammar/xtml.rs

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📝 Summary

Summary by CodeRabbit

• New Features
  • Added grammar generation for Kimi K3 XTML tool-call flows, covering call framing and entry paths.
  • Tool-call arguments now follow tool schemas, including required and optional properties, supported value types, and string-enum constraints. Local schema references are also supported.
  • Reasoning prefixes are generated from the format’s reasoning region; grammar generation remains unavailable when that region cannot be derived.

Walkthrough

Format grammar derivation now reads transition-table regions and block-entry paths, including XTML calls for Kimi K3. XTML grammar generation builds repeated tool-call blocks and schema-constrained arguments, with local definition handling and tests for alternate transitions and argument shapes.

Changes

Tool-call grammar derivation

Layer / File(s)	Summary
Format-table grammar derivation crates/symphony/src/format.rs, crates/symphony/src/grammar.rs	Format accessors expose state counts and transition rows. Grammar derivation identifies regions and block-entry paths from transitions, routes XTML formats to XTML generation, and tests reasoning prefixes, entry paths, and transition-order independence.
XTML calls and schema-derived arguments crates/symphony/src/grammar/xtml.rs	XTML generation builds one-or-more tool calls with schema-ordered arguments. Supported types and string enums constrain values. Local definitions are resolved for schema references.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant FormatGrammar
  participant call_markers
  participant region_helpers
  participant xtml_calls
  participant ToolSchemas
  FormatGrammar->>call_markers: Find argument and wrapper regions
  call_markers->>region_helpers: Inspect transition rows
  region_helpers-->>FormatGrammar: Return region markers and block-entry paths
  FormatGrammar->>xtml_calls: Pass markers, entry paths, and tool schemas
  xtml_calls->>ToolSchemas: Read properties and local definitions

Loading

Merge Risk: 🔵 Low · up to 307cb

Tool schemas that reference their root from a property can produce an invalid or incorrect call constraint. This narrow issue remains at the reviewed head; other integer arguments retain their intended constraint.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the Kimi K3 structural-tag derivation and its main implementation sources: table regions and the old builder's argument shapes.
Description check	✅ Passed	The description directly explains the XTML derivation, region-based paths, argument schemas, parity checks, and out-of-scope work.
Docstring Coverage	✅ Passed	Docstring coverage is 93.10% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 58 functions across 7 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[claude]

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[hello-alexmcc]

Rule-17 review of #2880 at 2884a0f: comment. I'll approve once the two open threads are answered. The Kimi K3 tag is right for the table it comes from, and the marker refactor changes no other table's grammar. Both of the bot's nits are real, though, and so is a third case of the same kind. Each is a short fix.

Kimi K3, derived by hand from the table:

• <|close|>message<|sep|> is the one terminal with a row from every state, and all five of its rows go back to message.
• The block is tools. It is entered from message, reasoning and content, so the ways in are "", <|close|>think<|sep|> and <|close|>response<|sep|>, in the old builder's order.
• The block's close is <|close|>tools<|sep|>. The call markers are <|open|>call tool=" and <|close|>call<|sep|>.

Parity with the old builder: a throwaway probe against KimiK3Parser::build_structural_tag, over 14 tool sets, both at_least_one values and both reasoning_open values. The sets cover:

• a declared order that isn't alphabetical, and every type;
• enums of strings, of numbers, mixed, and empty;
• type arrays and untyped properties;
• a property's own partial $defs, a # root pointer, nested $refs, definitions, and a $ref beside its own type;
• dangling $ref and $dynamicRef, escaped pointers, and a remote $ref;
• properties that isn't an object, and required naming a missing property;
• escaped and non-ASCII names, and an unnamed tool beside a named one.

Results:

• In all 56 payloads, the only difference is "type": "tag" on each tag, which the old K3 builder leaves out. The old GLM and DSML builders write it, so the engines take it today.
• reasoning_open changes nothing, as the old factory registered no reasoning prefix for K3.
• With no tools, or only unnamed ones, the old builder gave a call with any name. This gives None, as #2877 does for the other tables.

No other table moves: I dumped every table's grammar at main + #2877 and at main + #2880: 15 tables, both Qwen3 syntaxes included, 3 tool sets and both flags, 180 grammars in all.

• Only Kimi K3's 12 lines differ (None → the tag), and no grammar goes from a tag to None.
• My #2877 probe still gives 36 of 36 equal against the old GLM and DSML builders, the reasoning prefix included.

The open threads, and one more:

1. opener_of and row order (the bot's first thread): agreed. On the into_the_block fixture it returns </think> as the block's opener, and only json_calls ignoring the block hides that.
   • The fix that mirrors close_of: take the opener from the row whose source is a state the region's close goes back to.
   • For the ways in, take the row from each way's own state, so each close is paired with its own opener.
2. turn_close on Qwen 2.5 (the second thread): agreed. In a two-state table, a self-row plus an entry row reach "every state". Requiring the rows to land in state 0 matches the doc's "ends whatever is open", and Kimi K3's five message_close rows all do.
3. A way in with no close (mine): before_open maps a missing close to "". That way in then becomes the bare opener, which forces the calls inside a region the model never closed: the shape the module doc says the tag avoids. Kimi K3 has a close on every way in, but a future table without one would silently get that tag. Giving None there, as for a thought that doesn't close back, would keep it loud.

Gates. I ran them at 2884a0f merged on main 21d5e44, with Rust 1.98.0, its own target dir and -j 2; each exited 0:

• cargo +nightly fmt -p smg-symphony --check
• cargo clippy -p smg-symphony --all-targets --all-features -- -D warnings
• cargo test -p smg-symphony: 325 lib, 10 fixture, 7 contract and 5 README tests
• RUSTDOCFLAGS="-D warnings" cargo doc -p smg-symphony --no-deps

Rule 17:

• Fixture ids: none changed.
• Property tests: no new format.
• Protected paths: the crate's grammar and format, which this stream owns. Format::states() is pub(crate), so rule 18 isn't touched.
• Trailers: the author's Signed-off-by, and no AI trailer. For rule 27, the authors of the ported file's history (git log --follow), Keyang Ru and the LightSeek Foundation account, are both credited.
  • One question: that history's commits also carry Co-authored-by: Chen Hongtao and key4ng. If rule 27's "every author" counts co-authors, Chen Hongtao is missing. key4ng looks like Keyang Ru's GitHub address.
• Threads: two open (above).

[slin1237]

Round at 303e4b3, answering the two threads above and the review's third point: a way into the block from a state with no close of its own is no longer a bare opener. ways_into returns None there, so the block, and the tag, have no grammar for that shape yet, the same answer the prefix gives a thought that does not close back to where it opened (WayIn's doc says so). No current table changes: the ways in are the turn's own state (opener alone), the thought and the answer.

Rule 27, every author of the ported file: the old kimi_k3.rs history names two co-authors besides its authors, Chen Hongtao and key4ng; both are added to the squash body in the description, beside Keyang Ru and the LightSeek Foundation account, and the round's commit carries them too.

[hello-alexmcc]

Rule-17 re-review of #2880 at 303e4b3: comment. Round 3 is coming with the fixes below, and I'll approve it on sight if it holds.

Answered in this round, checked:

1. The block's opener comes from the state its close returns to (the bot's first thread). region() now pairs the two: a_blocks_opener_is_the_row_from_the_state_its_close_returns_to gets <calls>, and Kimi K3's rows in reverse give the same tag.
2. The turn's end returns to the turn's own state (the bot's second thread). Qwen 2.5's call_open no longer qualifies, and Kimi K3's five message_close rows all go to message.
3. Rule 27: Chen Hongtao and key4ng are now credited beside Keyang Ru, the LightSeek Foundation account and Chang Su, in the commit and in the squash body.

I withdraw my third point from round 1. The bot's new thread is right. A way in without a close of its own now gives None for every call syntax, though only XTML writes the ways in. Keying on state 0 also leaves MiniMax M3's content, the turn's own text after its thought, without a grammar for good. And my premise was wrong: every way in is a row the table has, so a bare opener from a state with no close is a legal way out of that state, not a call inside an open region.

My round-1 wording also caused a pairing bug, now fixed for round 3. I asked for "the row from each way's own state". But after a way's close the engine is in the state that close returns to, so the opener has to be that state's row into the block. Kimi K3 can't show the difference, because every row into tools is tools_open. The round's two_doors table under XTML shows it: the thought's way in begins </think><calls-from-thought> in both row orders, and no path in the table writes that.

The rule round 3 takes, for each state with a row into the block:

• the turn's own state: its own row's opener;
• a region with a close: the close, then the opener of the row from the state the close returns to;
• any other state: its own row's opener.

The ways in are computed where XTML writes them, so the other syntaxes don't depend on them.

Gates and probes at 303e4b3 merged on main 21d5e44, with Rust 1.98.0, its own target dir and -j 2:

• fmt, clippy and doc each exit 0.
• cargo test -p smg-symphony: 327 lib, 10 fixture, 7 contract and 5 README tests.
• Against the old builders: 36 of 36 equal for GLM and DSML. Kimi K3 is still equal in all 56 payloads but for "type": "tag".
• The 180-grammar dump is identical to 2884a0f's.

[slin1237]

Round 3 at 1a8c5b1, from the reviewer's notes on round 2 and the bot's thread above.

• After a thought's or an answer's close the engine stands in the state the close returns to, so the way into the block from there is that close and then the row into the block from that state (region() names its home; the region's own row when the home has none). The two-doors table under XTML now has the ways in <calls> and </think><calls>.
• Every way in is a path the table has. A state with no close of its own enters by its own row rather than denying the block a grammar: the turn's own state (state 0, which region() treats as no region, since the rows back into it close the regions it holds), and a state such as MiniMax M3's text after the thought. A thought's or an answer's region is read with the calls' states excluded, so its own row into the block is not taken for its close. The same way in is kept once, so MiniMax M3's three rows into its block make one way in, <tool_call>.
• The ways in are built only where they are read, in the XTML branch of grammar(); the other syntaxes no longer depend on them.

The reviewer's round-1 third point (a way in without a close gives None) is withdrawn by its author and undone here, for the reason above.

[hello-alexmcc]

Rule-17 re-review of #2880 at 1a8c5b1: approve. All three threads are answered and resolved. This round takes the rule from my round-2 review, and my checks pass at this head.

The ways in, checked by hand and by a throwaway probe under XTML:

• Kimi K3: <|open|>tools<|sep|>, <|close|>think<|sep|><|open|>tools<|sep|> and <|close|>response<|sep|><|open|>tools<|sep|>. The opener and the two closes are the triggers, as in the old builder.
• two_doors: <calls> and </think><calls>, in both orders of its rows into the block.
• MiniMax M3's real table, declared as XTML: one way in, <tool_call>, from all three states after deduplication. That's the bot's case, and it can now get a grammar once its syntax is derived.
• into_the_block: <calls> and </think> under XTML. Under JSON, a tag when the reasoning is closed and None when it's open, from the prefix path.
• Structure:
  • The ways in are built only for XTML, so the other syntaxes no longer depend on them.
  • A thought's or an answer's region is read without the calls' states, so a row into the block never counts as its close.
  • State 0 is no region.

Parity:

• Kimi K3 vs KimiK3Parser::build_structural_tag, over 14 tool sets and both flags: all 56 payloads are equal except for "type": "tag" on each tag, which the old GLM and DSML builders already write. With no tools, or only unnamed ones, the result is None, as for every table since #2877.
• Every table's grammar vs main + #2877, 180 grammars: only Kimi K3's 12 lines differ, and the dump is identical to 2884a0f's.
• My #2877 probe: 36 of 36 equal for GLM and DSML.

Gates. I ran them at 1a8c5b1 merged on main 21d5e44, with Rust 1.98.0, its own target dir and -j 2; each exited 0:

• cargo +nightly fmt -p smg-symphony --check
• cargo clippy -p smg-symphony --all-targets --all-features -- -D warnings
• cargo test -p smg-symphony: 328 lib, 10 fixture, 7 contract and 5 README tests
• RUSTDOCFLAGS="-D warnings" cargo doc -p smg-symphony --no-deps

Rule 17:

• Fixture ids: none changed.
• Property tests: no new format.
• Protected paths: the crate's grammar and format, which this stream owns. Format::states() is pub(crate), so rule 18 isn't touched.
• Trailers: the author's Signed-off-by, and no AI trailer. For rule 27, every author of the ported file's history is credited, co-authors included: Keyang Ru, key4ng, Chen Hongtao and the LightSeek Foundation account, with Chang Su. They appear in each commit and in the squash body.
• Threads: three, all answered and resolved.

The merge is the maintainer's (rule 25), after #2877.

[coderabbitai]

Actionable comments posted: 1

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Inline comments:
Review comments at @crates/symphony/src/grammar/xtml.rs:
- Around line 225-227: Update `resolve` so `#` and `#/` return `None` instead of
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📒 Files selected for processing (7)

• crates/symphony/src/format.rs
• crates/symphony/src/formats/ling.rs
• crates/symphony/src/grammar.rs
• crates/symphony/src/grammar/xtml.rs
• crates/symphony/src/lib.rs
• crates/symphony/src/tagged/dsml.rs
• crates/symphony/src/tagged/keyed.rs

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[slin1237]

@coderabbitai review

[claude]

🟡 Nit: Two docs went stale with 307cbdf. This one says each way in is "the state's close first when it has one", and the module doc (L29–L33) says "from a region with a close of its own, that close and then the row into the block". After this push, a state that has a close but whose home has no row into the block enters by its own row, with no close. That's the mid_thought test: the thought has </think> but its way in is just <calls>. WayIn and ways_into were updated; these two weren't.

"so it is the same either way" also stops holding for that table. The XTML branch returns before reasoning_open is checked, so mid_thought.grammar(.., reasoning_open = false) still gives a single trigger, <calls>. But with the thought closed the model sits in content, and content has no row on <calls>. The only path the table has is <think><calls>. So the tag would force a block the parser reads as plain content. The new test only runs reasoning_open = true.

No shipped table hits this, since every Kimi K3 state has a row into tools. Possible fixes:

• Narrow the claim in both docs to tables where every state the prompt can leave the model in has a way in.
• Or, in the XTML branch, return None when the state reasoning_open implies (the thought, or the turn's own state otherwise) has no way in. That also pins the reasoning_open = false case of mid_thought in a test.

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