Fix #6605 mutation error type Int32 scalar resolution

[michaelstaib]

• add a regression test for AddMutationErrorConfiguration with a custom error record containing int
• ensure late-registered mutation error types can normalize runtime and scalar references by registering runtime bindings
• eagerly infer/register member output types for non-exception custom error objects so scalar types used only in those errors are available

Fixes #6605

[github-actions]

Fusion Gateway Performance Results

Simple Composite Query

	Req/s	Err%
Constant 2 (50 VUs)	3134.34	0.00%
Ramping 2 (0-500-0 VUs)	3834.79	0.00%

Response Times

	Min	Med	Avg	P90	P95	Max
Constant 2	1.14ms	12.90ms	15.65ms	25.92ms	35.88ms	260.37ms
Ramping 2	1.10ms	51.22ms	56.97ms	100.03ms	142.94ms	286.17ms

---

Deep Recursion Query

	Req/s	Err%
Constant 2 (50 VUs)	758.81	0.00%
Ramping 2 (0-500-0 VUs)	941.33	0.00%

Response Times

	Min	Med	Avg	P90	P95	Max
Constant 2	11.55ms	57.16ms	63.55ms	81.93ms	99.65ms	766.05ms
Ramping 2	3.00ms	202.41ms	219.83ms	441.33ms	492.30ms	1006.12ms

---

Variable Batching Throughput

	Req/s	Err%
Constant 2 (50 VUs)	5848.86	0.00%
Ramping 2 (0-500-0 VUs)	4927.35	0.00%

Response Times

	Min	Med	Avg	P90	P95	Max
Constant 2	0.16ms	7.96ms	8.45ms	14.05ms	17.23ms	59.11ms
Ramping 2	0.17ms	41.54ms	46.61ms	88.01ms	115.86ms	264.26ms

---

Runner 2 = benchmarking-2

Run 22489690792 • Commit 4569905 • Fri, 27 Feb 2026 14:24:11 GMT

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (bb123ab) to head (8d8c79a).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@     Coverage Diff      @@
##   main   #9252   +/-   ##
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