test: harden G2 conformance invariants

[BunsDev]

Summary

• restore the full signed 64-bit content metadata range while preserving JSON-safe cursor boundaries
• make reusable conformance and property suites authority-opaque for session identifiers
• fail fast on stalled or overshooting cursors and bind every returned reconciliation to the unchanged durable adoption
• strengthen request-digest properties with durable-state invariants

Test plan

• PROPTEST_CASES=2048 cargo test -p psyche-coven -p psyche-test-support
• cargo clippy -p psyche-coven -p psyche-test-support --all-targets -- -D warnings
• python3 scripts/check-g2-evidence-test.py -q

[Copilot]

Pull request overview

This PR strengthens the G2 conformance and property-test suites by removing hard-coded assumptions about session identifiers, asserting stronger durability invariants (especially around reconciliation and request-digest mismatches), and expanding content-size validation to the full signed 64-bit range.

Changes:

• Introduces scripted_fixture_with_session_id and updates suites/tests to accept opaque, caller-chosen session IDs.
• Hardens invariants around reconciliation and request-digest mismatch handling to ensure durable adoption state is not mutated by failed/forged operations.
• Expands ContentAddressedReference size validation from JS safe-integer bounds to i64::MAX, and updates tests accordingly.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
crates/psyche-test-support/tests/state_machine.rs	Updates state-machine property tests to use opaque session IDs and to assert durable adoption invariants across reconciliation and digest-mismatch paths.
crates/psyche-test-support/tests/conformance.rs	Adds a conformance test ensuring all reusable suites pass with an opaque (non-session-1) session id.
crates/psyche-test-support/src/suites/mod.rs	Re-exports scripted_fixture_with_session_id for suite consumers.
crates/psyche-test-support/src/suites/coven.rs	Implements configurable session IDs in the scripted fixture and strengthens cursor/reconciliation/adoption durability assertions; updates max content-size expectations.
crates/psyche-test-support/src/lib.rs	Re-exports scripted_fixture_with_session_id at the crate root.
crates/psyche-coven/tests/bindings.rs	Updates binding tests to match the new i64::MAX content-size boundary.
crates/psyche-coven/src/port.rs	Changes ContentAddressedReference validation to allow up to i64::MAX bytes and rejects overflow beyond that.

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