[fjc9]

Problem

A grammar repetition of exactly MAX_REPETITION_THRESHOLD (2000) crashes with an uncaught std::runtime_error, while both 1999 and 2001 work:

• "a"{0,1999} → parses and expands normally
• "a"{0,2001} → the parse-side clamp in parse_sequence kicks in (max_times > MAX_REPETITION_THRESHOLD → unbounded), so it parses
• "a"{0,2000} → passes the parse-side check (2000 is not > 2000), then handle_repetitions throws because its guard uses >=:

if (n_prev_rules * total_rules >= MAX_REPETITION_THRESHOLD) {
    throw std::runtime_error(...);
}

The practical impact: any JSON schema with "maxLength": 2000 (a very natural round number to pick) makes json_schema_to_grammar emit .{0,2000} and aborts the process, e.g. via llama-completion -j '<schema>':

libc++abi: terminating due to uncaught exception of type std::runtime_error:
failed to parse grammar

This is the boundary case of #25746, and appears to be an off-by-one left over from the clamp introduced for #27087: the two checks disagree about whether the threshold value itself is allowed.

Fix

Make handle_repetitions agree with the parse-side clamp by using a strict comparison, so the threshold value itself expands normally. Values above the threshold keep their existing behavior (clamped to unbounded at parse time for a single repetition, rejected for nested products).

Tests

Added to tests/test-grammar-parser.cpp:

• "a"{0,2000} and "a"{2000} must parse (previously failed)
• ("a"{0,50}){0,50} (nested product 2500 > threshold) must still be rejected

Verified locally on macOS (arm64): the new tests pass, the previously crashing JSON schema ("maxLength": 2000) now generates valid constrained output, and the nested-product rejection still triggers.

🤖 Generated with Claude Code

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