qCompute — Replay Engine

File: qc_Replay.md
Layer: RTT‑Inside Compute Harness
Status: Canonical (2026)

The Replay Engine is the final authority of qCompute.

Replay reconstructs:

session
frames
operators
transitions
drift
routing
backend legality
environment sequence
hash chain integrity

Replay verifies that the .qtrace ledger is complete, valid, and canonical.

qCompute computes structure, not amplitudes.

1. Purpose#

Replay:

reads the .qtrace file
reconstructs the entire session deterministically
verifies all invariants
verifies all routing decisions
verifies all drift calculations
verifies all transitions
verifies all frame boundaries
verifies all backend legality
verifies all environment legality
verifies the hash chain

Replay is read‑only and authoritative.

2. Replay Inputs#

Replay receives:

.qtrace file:
  header
  operator entries
  frame summaries
  transitions
  footer
  hash chain root

All fields are required.

3. Replay Reconstruction Model#

Replay reconstructs the session by:

reading operator stream
applying Validator rules
applying Router rules
applying Frame Manager rules
applying Drift Engine rules
applying Transition Engine rules
verifying capture metadata
verifying hash chain integrity

Replay must produce the same structural session that was originally executed.

4. Operator Reconstruction#

For each operator:

Replay verifies:

grammar
arguments
tier legality
backend legality
environment legality
token requirements
routing reason
frame action
drift metadata
timestamps
hash chain links

Replay recomputes:

backend
routing reason
frame action
drift predicted
drift measured
drift accumulated

Replay must match capture exactly.

5. Frame Reconstruction#

Replay reconstructs frames by:

opening frames on routing triggers
closing frames on routing triggers
enforcing tier monotonicity
enforcing backend consistency
enforcing drift bounds
enforcing environment consistency

Replay verifies:

frame boundaries
frame drift summaries
frame backend summaries
frame timestamps

Frames must match capture exactly.

6. Transition Reconstruction#

Replay reconstructs transitions by:

reading transition entries
verifying legality
verifying token usage
verifying environment sequence
verifying drift reset
verifying frame closure
verifying backend legality

Replay must confirm:

sandbox → production → archive
no illegal transitions
archive is terminal

7. Drift Reconstruction#

Replay recomputes drift:

drift_total = Σ drift_measured

Replay verifies:

drift never exceeds bound
drift overflow events match capture
drift resets match frame boundaries
drift summaries match operator accumulation

Drift must match capture exactly.

8. Backend Reconstruction#

Replay verifies:

backend legality
tier binding
environment legality
backend changes
backend summaries

Backend must match capture exactly.

9. Hash Chain Verification#

Each operator and transition includes:

hash_prev: "<sha256>"
hash_self: "<sha256>"

Replay verifies:

hash_prev matches previous entry
hash_self matches recomputed hash
final hash matches footer root

If hash chain invalid:

replay_valid: false
reason: "hash chain invalid"

10. Replay Metadata#

Replay produces:

replay:
  valid: true|false
  reasons: [...]
  reconstructed_session: {...}

Reasons include:

"illegal operator"
"illegal transition"
"tier violation"
"backend violation"
"environment violation"
"drift violation"
"hash chain invalid"
"capture mismatch"

11. Invariants#

Replay enforces:

grammar correctness
argument correctness
environment legality
backend legality
tier monotonicity
drift bounds
routing correctness
transition correctness
token requirements
frame boundaries
archive terminality
hash chain integrity

Replay is the final arbiter of structural truth.

12. Summary#

The Replay Engine:

reconstructs the entire session
verifies every structural decision
enforces all invariants
validates the hash chain
ensures the .qtrace file is canonical

Replay is the authoritative verifier of qCompute.