Validator error message references non-existent parameter `bc_{dir}%Tw_out` (should be `Twall_out`)

[sbryngelson]

In toolchain/mfc/case_validator.py, the isothermal-out wall-temperature positivity check prints a parameter name that does not exist. The value is correctly fetched as bc_{dir}%Twall_out, but the error string in the prohibit call says bc_{dir}%Tw_out:

# line 1366 — correct fetch
tw_out = self.get(f"bc_{dir}%Twall_out")
# line 1367 — correct message
self.prohibit(tw_out is None, f"Isothermal Out (bc_{dir}%isothermal_out) requires a wall temperature to be set (e.g., bc_{dir}%Twall_out).")
if tw_out is not None and self._is_numeric(tw_out):
    # line 1369 — WRONG name in the message
    self.prohibit(tw_out <= 0.0, f"Wall temperature bc_{dir}%Tw_out must be strictly positive for thermodynamics (got {tw_out}).")

The actual parameter is Twall_out, defined in toolchain/mfc/params/definitions.py:86 ("Twall_out": "Temperature of the exit-side isothermal wall."); there is no Tw_out parameter anywhere. The parallel Twall_in branch (line 1356) correctly prints bc_{dir}%Twall_in.

Impact. A user who sets a non-positive exit wall temperature gets an error telling them to fix bc_x%Tw_out, a parameter that doesn't exist — misdirecting the fix. Diagnostic-message-only; no validation logic is affected.

Fix. Change bc_{dir}%Tw_out to bc_{dir}%Twall_out on line 1369.

Output-neutral / golden-file-safe. Yes — error-message string only.

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_{Filed from a repo-wide code-cleanliness review; locations verified against master @ 40dde5e.}

Code references

• toolchain/mfc/case_validator.py:1366-1369 — fetch Twall_out, wrong message Tw_out
• toolchain/mfc/params/definitions.py:86 — Twall_out definition