[AdaWorldAPI]

#1837 made a sparse write skip absent lanes, but over a fixed lab layout. This replaces that layout with one each class declares at compile time. The ClassView resolves it once per class.

Contract: lane_codec (new, zero-dep, additive)

• EpiLaneSpec holds:
  • width (8 or 9 bits);
  • code space (Sym / Asym);
  • value offset;
  • presence offset;
  • lane count.
• Compile-time choice. A consumer states the layout as EpiLaneClass::SPEC, built with checked(), so an invalid layout fails to compile (a compile_fail doctest pins this).
• The presence plane is mandatory. A lane is absent (NaN, $null, UNKNOWN) when its presence bit is 0 and its value is 0. This holds at 8 and 9 bits alike, and it is the only absent code.
  • At 9 bits the presence bit is also the sign, so presence 0 with a nonzero magnitude is a negative value (DR512, matching ndarray codec9).
  • A 9-bit lane must be Sym.
• ONNX QuantizeLinear / TFLite annotations choose the code space through CodeSpace::from_zero_point (zero point 0 = Sym).
• ClassView::epi_lanes(class) names the same constant for a classid. The default None means undeclared, and binding refuses, as epistemic_reading already does.

Probe

• Bind once. ThoughtTables::bind_lanes::<L>(view, class) checks the ClassView once. It returns a LaneBinding<L>, or Refusal::LaneLayout when the class declares no layout or a different one.
• Writes take the binding. write_epi(&binding, …) does not look the class up again.
• Sharing a binding. A binding shared across threads belongs in a OnceLock set when the registry loads. LazyLock doesn't fit, because its initializer cannot take the view.
• 9-bit lanes still go through EpiLane9::never_touched, and a test checks that the contract rule and codec9 agree on all 512 codes.

Tests

• Contract, 7 unit tests and 2 doc tests:
  • each validation rule refuses;
  • adjacent regions pass;
  • absent is exactly one of the 512 (value, presence) pairs;
  • presence bits past the first byte are read;
  • zero point maps to code space.
• Probe, 19 tests in all:
  • binding refuses an undeclared or different layout;
  • an absent lane is not written (DR512 and ONNX uint8);
  • the thought's own earlier value is kept;
  • a 9-bit negative is written;
  • a computed −0.499 is written as +0;
  • an absent lane beside a change leaves only the change stored;
  • an asym code 0 is written;
  • a sym int8 code −128 with presence 1 is a value.
• Eight disables, each red: bind check, keep step, presence-bit copy, presence-only test, value-only test, presence byte offset, overlap check, 9-bit Asym.
• Other checks:
  • the contract's full suite passes;
  • contract clippy (-D warnings) and cargo fmt --check are clean;
  • clippy reports nothing in the probe.

Open

Mapping the 32-bit row classid to ClassView's u16 ClassId is left to the caller; the probe takes ClassId as an argument instead of doing bit math on the key.

Board: .claude/board/entries/2026-10-28-lane-layout-from-classview.md.

🤖 Generated with Claude Code

https://claude.ai/code/session_01XAqKMPWTwovjYJEUMuGPb4

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[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-28T18:01:15.154992Z	c393f65	Draft marked ready

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Prevent offset overflow before validating slab bounds

When validate() is called at runtime with an offset near u16::MAX, these additions overflow before the bounds checks run. For example, a Bits8/Sym spec with values: 65535, presence: 96, and lanes: 16 returns Ok(()) in an optimized build, despite lying outside the 512-byte row; reading a value through that accepted spec then panics. Debug builds instead panic during validation rather than returning SpecError::OutOfSlab. Widen the arithmetic or use checked addition so invalid offsets are consistently refused.

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