Tighten Kani proof bounds for solver tractability#111
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The first scheduled Kani run to include prop-amm (13 Jul) hit the GitHub-hosted runner's 6-hour hard limit: every other crate's proofs finished in under 3 minutes, but prop-amm's "Run Kani" step ran from 07:08 to 13:08 and was killed, surfacing as a cancelled run. The culprit is proof_quote_brackets_oracle, which left the oracle price at the full u64 range while multiplying it by the symbolic spread — a 64x14-bit nonlinear multiply plus 128-bit divisions, the worst case for the bit-precise solver (the old comment called this "linear", but both operands are symbolic). Cap the price at 16 bits: the rounding identities depend only on the product's residue mod 10_000, which a 16-bit price against the full spread range already covers exhaustively. Also tighten the symbolic-divisor harnesses (buy/sell to 8-bit amounts/prices, the chained round trip to 6-bit) to match the bounds the other finance proof crates stay tractable with, and give the verify job a 45-minute timeout so a blown-up harness fails fast and loudly instead of burning 6 hours and showing up as "cancelled". Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01FYjBwE7n8i1J3ycYD8ebup
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Summary
This PR improves the tractability of Kani formal verification proofs by tightening symbolic value bounds in the prop-amm crate and adding a CI timeout to catch runaway verification jobs.
Key Changes
Quote bracket proof (
proof_quote_brackets_oracle): Increased price bound from unbounded u64 to 16-bit (0xFFFF) with detailed explanation of why this exercises all rounding edges without sacrificing coverage. The previous unbounded price caused the harness to run for hours.Buy/sell oracle value proofs: Reduced amount and price bounds from 1023 to 255 (8-bit) to align with solver tractability limits used in other finance proof crates. Updated comments to explain that symbolic divisor bit-width significantly impacts solver cost.
Round-trip profit proof: Further tightened bounds to 63 for both amount and price, as this harness chains two symbolic divisions and requires stricter constraints.
CI timeout: Added a 45-minute timeout to the Kani proof job to fail fast and loudly when harness bounds cause the solver to blow up, rather than silently hitting the 6-hour runner limit and appearing as a "cancelled" run.
Implementation Details
The changes are grounded in the observation that:
https://claude.ai/code/session_01FYjBwE7n8i1J3ycYD8ebup