[davrens101]

Problem

Qubit design reporting aliases the SciPy solution vector and replaces optimization targets with derived physical quantities. All-fixed Xmon optimization can return a read-only vector and crash during this reporting step. Floating-transmon reporting mutates the vector before recomputing its objective, understating the residual against the original constraints; its returned cost is also a one-element set rather than a number.

Change

• Copy the solution before substituting report values in both designers.
• Use the optimizer's saved objective (sol.fun) for reporting, without evaluating an altered vector.
• Return a numeric cost_error_% from floating-transmon optimization.
• Document the cost semantics and add real-SciPy, fixed-constraint regressions.

No optimizer algorithm, objective, physical formula, public signature or Xmon return convention changes.

Verification

• Before: all-fixed Xmon raises ValueError: assignment destination is read-only; floating-transmon reporting gives 48.73865330737892 instead of the independently calculated 140.26009493027976 percent, and returns a set.
• After: actual Xmon optimization completes with cost 80.76048600418196 percent; floating-transmon cost equals 140.26009493027976 and its result serializes to JSON.
• python -m pytest -q UnitTests/test_qubit_optimisation.py UnitTests/testBasicQiskitMetal.py: 4 passed. Existing initial-guess-outside-bounds SciPy warning and two dependency deprecation warnings remain; they are not suppressed.
• New-test Ruff check/format and changed Python compile checks pass. Independent read-only AI review found no blocker.
• Windows/Python 3.11, CPU only. No full-suite or external EM-solver validation claimed.

Review and assistance

Human review: davrens101 confirmed reviewing the work live before submission. AI assistance was used for investigation, implementation and verification. No maintainer review or approval is claimed. Verification was CPU-only; no GPU validation is claimed.

[davrens101]

I cherry-picked the four independent SQDMetal fixes (#91-94) onto their shared upstream base and they apply cleanly together. Parser, LC, optimizer, transmon and the existing component geometry tests: 14 passed, 21 subtests passed. The optimizer/JSON run and a 61-state charge-basis Hamiltonian check also pass. With #94's corrected energy physics the floating original-target cost becomes 131.30895980700444 and still matches the independently calculated residual. CPU only, existing warnings not suppressed, no full suite or external EM solver.