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+---
+name: "Adr 0007 Projection Replay"
+description: "Projection purity and replay determinism contract"
+depth: 2
+links: ["../index.md", "../modules/core-events-submodule-spec.md", "./adr-0006-event-store-append-only.md"]
+---
+
+# ADR-0007: Projection & Replay Determinism Contract
+
+**status:** accepted
+**date:** 08.05.2026
+**deciders:** Kami
+
+---
+
+## context
+
+Projections and replay are responsible for reconstructing system state from event streams. Any nondeterminism in projection logic or replay execution breaks system consistency guarantees.
+
+The system requires strict guarantees that state reconstruction is reproducible across time, environment, and implementation.
+
+This ADR formalizes projection and replay correctness requirements.
+
+---
+
+## content
+
+### 1. projection purity
+
+* Projection MUST be a pure function:
+  `EventStream → State`
+* no hidden state or external dependencies are allowed
+* projections MUST NOT mutate shared state
+
+### 2. determinism requirement
+
+* identical event streams MUST produce identical state
+* ordering of events MUST be respected (sequence order)
+
+### 3. replay invariance
+
+* replay MUST produce identical results regardless of:
+
+    * runtime environment
+    * execution timing
+    * storage backend implementation
+
+### 4. environment independence
+
+* replay MUST NOT depend on:
+
+    * live services
+    * LLM calls
+    * external APIs
+* replay MUST be fully deterministic offline
+
+### 5. disposable projections
+
+* projection state MUST be rebuildable at any time
+* no projection state is authoritative; only event log is
+
+---
+
+## consequences
+
+**positive:**
+
+* enables safe rebuild of entire system state
+* guarantees consistency across infrastructure implementations
+* simplifies debugging (full replayability)
+* enables future snapshotting and caching layers
+
+**negative:**
+
+* prohibits non-deterministic projection logic
+* forces strict separation of computation vs external effects
+* requires careful handling of ordering assumptions
+
+---
+
+## status
+
+accepted