RUN-CSTR-01: Decide on /v1/run constraints tests

[Talchain]

Problem

Tests in tests/constraints.test.ts are failing because they expect /v1/run to support constraints validation, but the current implementation doesn't handle constraints.

Failing tests:

• Constraints on /v1/run > rejects bounds violation (min)
• Constraints on /v1/run > rejects bounds violation (max)
• Constraints on /v1/run > rejects forbidden edge
• Constraints on /v1/run > accepts graph with allowed edges
• Constraints on /v1/run > rejects bounds on non-existent node
• Constraints on /v1/run > accepts valid bounds

Options

1. Move tests to /v1/optimise: Constraints are already fully implemented there
2. Add minimal constraints passthrough: Return 400 with helpful message pointing to /v1/optimise
3. Implement full constraints support: Add validation to /v1/run handler

Acceptance Criteria

ACCEPT:RUN_CSTR tests=green behaviour=documented no_regression=true

• Tests pass without lowering standards
• Behaviour clearly documented
• No performance regression
• Decision documented in code comments

Impact

Current pass rate: 98.1% (761/776)
Target pass rate: ≥98.5%
Tests affected: 6