Initial support for leakage

[david-pl]

Adds support for leakage on GeneralizedTableau by replacing the is_lost: Vec<bool> by an enum. Leaked qubits are fixed to either 0 or 1 depending on the given probabilities and are detected as such.

Note, that GeneralizedTableauSum does not support leakage yet.

[github-actions]

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[Copilot]

🟡 Changes recommended

A compile-breaking invalid import was introduced (use std::debug_assert;) and should be fixed before merging.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR adds initial leakage support to the GeneralizedTableau simulation stack by introducing a per-qubit status enum (live/leaked/lost), extending the Stim parser/executor to handle I_ERROR[leakage](p0, p1), and exposing leakage state through the Python bindings.

Changes:

• Introduces QubitStatus to represent Live / Leaked / Lost, and updates gate/noise behavior to skip non-live qubits while preserving distinct measurement behavior for leakage vs loss.
• Extends stim-parser + ppvm-stim to parse/lower/print/execute the leakage tag on I_ERROR.
• Exposes is_leaked() / leakage_values() through Python bindings and adds Python/Rust tests for leakage behavior.

File summaries

File	Description
ppvm-python/test/generalized_tableau/test_stim.py	Adds Stim-driven leakage execution tests
ppvm-python/test/generalized_tableau/test_loss.py	Adds Python API tests for leakage state helpers
ppvm-python/src/ppvm/generalized_tableau.py	Adds Python-facing is_leaked / leakage_values
ppvm-python/src/ppvm/_core.pyi	Updates core stub with leakage APIs
crates/stim-parser/tests/tags.rs	Tests parsing of leakage tag args
crates/stim-parser/tests/roundtrip.rs	Adds leakage to roundtrip corpus
crates/stim-parser/tests/proptest_parse.rs	Adds [leakage] token to proptests
crates/stim-parser/tests/proptest_ast.rs	Generates ExtendedInstruction::Leakage in proptests
crates/stim-parser/tests/extended.rs	Tests lowering/tag validation for leakage
crates/stim-parser/src/print/mod.rs	Prints leakage instruction canonically
crates/stim-parser/src/pipeline/lower.rs	Lowers I_ERROR[leakage] into extended AST
crates/stim-parser/src/ast/extended.rs	Adds ExtendedInstruction::Leakage variant
crates/ppvm-traits/src/traits/noise.rs	Adds leakage-related noise traits
crates/ppvm-traits/src/traits/mod.rs	Re-exports leakage traits from traits module
crates/ppvm-tableau/tests/gates.rs	Updates tests for qubit_status replacing is_lost
crates/ppvm-tableau/src/qubit_status.rs	New enum + helpers for live/leaked/lost handling
crates/ppvm-tableau/src/noise.rs	Implements leakage channel + updates loss logic for status
crates/ppvm-tableau/src/measure.rs	Updates lost-measurement check for status
crates/ppvm-tableau/src/measure_all.rs	Updates measure-all lost checks for status
crates/ppvm-tableau/src/lib.rs	Exposes qubit_status module + prelude export
crates/ppvm-tableau/src/gates/tgate.rs	Skips T gates on inactive (lost/leaked) qubits
crates/ppvm-tableau/src/gates/rot2.rs	Updates rot2 fallback/skip logic for inactive qubits
crates/ppvm-tableau/src/gates/rot1.rs	Skips rot1 on inactive qubits
crates/ppvm-tableau/src/gates/reset.rs	Prevents reset from re-zeroing leaked qubits
crates/ppvm-tableau/src/gates/clifford.rs	Skips Clifford ops on inactive qubits; batch filtering updates
crates/ppvm-tableau/src/display.rs	Updates display output to show qubit_status
crates/ppvm-tableau/src/data.rs	Replaces is_lost storage with qubit_status
crates/ppvm-tableau-sum/src/storage/vec.rs	Adapts storage sizing to qubit_status
crates/ppvm-tableau-sum/src/storage/mod.rs	Adapts hashing/equality to qubit_status
crates/ppvm-tableau-sum/src/storage/map.rs	Adapts mask sizing to qubit_status
crates/ppvm-tableau-sum/src/noise.rs	Updates loss branching to write QubitStatus::Lost
crates/ppvm-tableau-sum/src/measure.rs	Updates lost checks to use is_lost() method
crates/ppvm-tableau-sum/src/data.rs	Updates tests for qubit_status instead of is_lost
crates/ppvm-tableau-sum/benches/parallelization_test.rs	Updates bench to use is_lost()
crates/ppvm-stim/tests/executor.rs	Adds executor tests for leakage behavior
crates/ppvm-stim/src/validate.rs	Allows leakage instruction through validation
crates/ppvm-stim/src/executor.rs	Executes leakage instructions via leakage_channel
crates/ppvm-stim/benches/stim-circuits.rs	Counts leakage targets for required-qubits computation
crates/ppvm-python-native/src/interface_tableau.rs	Exposes leakage state through Python native interface
crates/ppvm-python-native/ppvm_python_native.pyi	Updates native stub with leakage APIs

Review details

• Files reviewed: 40/40 changed files
• Comments generated: 3
• Review effort level: Lite

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[Copilot]

🔵 Needs a closer look

It changes core simulator state semantics across multiple crates/languages (tableau, stim parsing/execution, Python bindings), warranting final human review despite strong test additions.

Review details

• Files reviewed: 40/40 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

🔵 Needs a closer look

It changes core simulator semantics across multiple Rust crates and the Python binding surface, so a final human review is needed to confirm correctness of the leakage model end-to-end.

Review details

Suppressed comments (1)

crates/ppvm-tableau/src/data.rs:789

• Same as above: any_lost now includes leaked qubits via is_inactive, so the name is inaccurate and can cause confusion when reasoning about leakage behavior.

        let any_lost = (0..count).any(|i| {
            let c = word_c * bits_per_word + base_bit_c + i;
            let t = word_t * bits_per_word + base_bit_t + i;
            self.is_inactive(c) || self.is_inactive(t)
        });

• Files reviewed: 40/40 changed files
• Comments generated: 2
• Review effort level: Lite

[Copilot]

🟢 Approval recommended

The leakage feature is implemented end-to-end (parser → executor → tableau → Python bindings) with targeted tests covering the new behavior and updated loss/leakage interactions.

Review details

• Files reviewed: 40/40 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

🔵 Needs a closer look

The change spans core simulator semantics, Stim parsing/execution, and Python bindings, so it warrants final human review despite strong test coverage.

Review details

Suppressed comments (2)

Previously missed (1) — in code that hasn't changed since the last review.

crates/ppvm-tableau-sum/src/storage/mod.rs:160

• Doc/comments for phase_loss_hash still refer to is_lost, but the code now uses qubit_status. This is misleading (and qubit_status can represent more than just loss). Update the wording to reflect that this hash tracks the loss state via qubit_status and fix the inline len() comment accordingly.

This issue also appears on line 317 of the same file.

crates/ppvm-tableau-sum/src/storage/mod.rs:319

• The BranchMutation::Loss doc comment still mentions the removed is_lost field; it should describe the new qubit_status representation so future readers don't look for a non-existent boolean vector.

        BranchMutation::Loss { q } => {
            tab.qubit_status[q] = QubitStatus::Lost;
        }

• Files reviewed: 41/41 changed files
• Comments generated: 0 new
• Review effort level: Lite