fix: constrain internal flag in deferral inner circuit also

[stephenh-axiom-xyz]

Resolves INT-9263.

[github-actions]

group	app.proof_time_ms	app.cycles	leaf.proof_time_ms
fibonacci	(-4 [-0.2%]) 1,680	12,000,265	(-2 [-0.5%]) 368
keccak	(+67 [+0.7%]) 9,585	18,655,329	(-17 [-1.1%]) 1,547
sha2_bench	5,358	14,793,960	(+14 [+2.4%]) 600
regex	(-5 [-0.7%]) 692	4,137,067	216
ecrecover	(-1 [-0.2%]) 429	123,583	(-2 [-1.1%]) 187
pairing	(-22 [-3.7%]) 568	1,745,757	(+1 [+0.5%]) 194
kitchen_sink	(-3 [-0.1%]) 2,297	2,579,903	(+2 [+0.4%]) 494

Note: cells_used metrics omitted because CUDA tracegen does not expose unpadded trace heights.

Commit: 122958c

Benchmark Workflow

[github-actions]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.