Prove an AI migration didn't change what your software does.
Strust runs the legacy system and its AI-written replacement on the same inputs, pinpoints the first behavior that diverged, and hands the evidence to both the coding agent and human reviewer.
Same input. Different branch. One-cent ledger change.
Interactive v1 demonstrator
Agent + reviewer viewsOne change. The agent fixes it; the reviewer decides it.
Agent view isolates the first changed decision and the next patch. Reviewer view translates that evidence into impact and a human decision. This controlled example illustrates the intended product loop; the published paper documents the current evidence and limits.
Agent receives
Trace-local cause, the first divergent decision, a suggested patch, and the exact rerun command.
Agent diagnosis / F-02
12 divergent tracesFirst divergence: Branch action
Batch branch B-17 / null-account path · Trace 417 / 1,215
Reference system
COBOL
IF ACCOUNT-ID = SPACES
NEXT SENTENCE
ELSE PERFORM WRITE-CLAIM
END-IF
Candidate system
Java
if (accountId == null) {
writeFallback(claim);
} else { writeClaim(claim); }
batch.advance();
Execution checkpoints
Source value / target value
NULL
Account input
NULL
Equivalent
TRUE
Guard B-17
TRUE
Equivalent
SKIP_WRITE
Branch action
WRITE_FALLBACK
Origin
0
Rows emitted
1
Changed
4,808
Batch count
4,809
Changed
The first changed decision is Branch action: the source returns SKIP_WRITE while Java calls writeFallback.
Capture → Compare → Isolate → Patch → Rerun
Migration was the first proving ground.
01 CUSTOMER-CODE PIC X(8). IF CUSTOMER-CODE = 'VIP' MOVE 'PRIORITY' TO QUEUE-NAME
String code = record.customerCode();
if (code.equals("VIP")) { // ← flagged
queueName = "PRIORITY";
}A legacy system is already an executable reference. Strust turns representative source behavior into evals for the system replacing it. Here, COBOL pads the shorter fixed-width value; Java treats VIP····· and VIP as different strings. Both compile; the behavior changes.
A benchmark for whether migration agents preserve behavior.
SemaMig-Bench · Benchmark v1
Run the source. Run the migration. Score the behavior.
SemaMig-Bench turns COBOL-to-Java migration into a paired, held-out evaluation. The same workload runs against the executable source and native Java candidate; a task passes only when the contract-relevant observations agree.
Protocol
Published
Five-page design and preregistered evaluation protocol
Task corpus
In construction
50 tasks planned across diagnostic, workflow, and system tiers
Leaderboard
Results forthcoming
Baseline scores publish after the v1 corpus and verifiers are frozen
Seeking design partners
Bring one real migration into the loop.
Strust is looking for engineering teams, modernization firms, and coding-agent builders with an important software change to verify. Bring the workflow; we will map the behavior that matters and show where the candidate diverges.
1.Define the behaviors and side effects that matter
2.Run the reference and candidate under one contract
3.Review retained evidence and the first divergence
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