wip: T0.6 EventLog redb backend (in progress, salvaged before restart)

.agent-progress

@@ -0,0 +1 @@
+T0.2

poimen/crates/log/Cargo.toml

@@ -5,9 +5,19 @@ edition.workspace = true
 authors.workspace = true
 license.workspace = true
 
+[features]
+default = []
+test-hooks = ["dep:tempfile"]  # enables the panic hook for T0.6 verification only
+
 [dependencies]
 ids.workspace = true
 serde.workspace = true
 serde_cbor.workspace = true
+redb.workspace = true             # redb v2.x with ACID write transaction
+async-trait.workspace = true      # EventLog trait must be async because backend may use it for async IO paths in P2
+tempfile = { version = "3", optional = true }  # only used by test-hooks feature to set CRASH_POINT env
 
 [dev-dependencies]
+env_logger = "0.11"
+once_cell = "1.19"
+log = "0.4"

poimen/crates/log/src/backend.rs

@@ -0,0 +1,27 @@
+// RedBEventLog — EventLog backend over redb atomic-commit protocol (4 tables, 1 txn).
+
+use crate::eventlog::{
+    CommitBatch, ConsumerPosition, EventLogError as _, LogReadOptions, OutboxEntry, StateDelta,
+};
+use async_trait::async_trait;
+use ids::serde_cbor_schema_tabledef::Type as RedbTableDef;
+use serde::{Deserialize, Deserializer, Serialize};
+
+/// Column name constants for the four tables of our atomic-commit protocol. Each one is a stable
+/// storage identifier — never change these between versions, otherwise any persisted record becomes unreadable across updates.
+const T_EVENTS:          &str = "EVENTS";
+const T_RUN_STATE:       &str = "RUN_STATE";
+const T_CONSUMER_POSN:   &str = "CONSUMER_POSITION";
+const T_OUTBOX:          &str = "OUTBOX";
+
+/// Hook used by tests compiled under `test-hooks`. Each call disables atomicity for the next commit() write — i.e., after writing event_log but before run_state, the process panics. This is what we use to prove T0.6's contract: if you read at recovery time in that exact window, *nothing* should be there (because nothing should have been committed).
+static HOOK_ENABLED: std::sync::atomic::AtomicU32 = core::sync::atomic::AtomicU32::new(0);
+
+#[derive(Debug)]
+pub struct RedBEventLog { _db: (), }  // placeholder — the db field is hidden; test-hooks use env-based signal
+
+impl std::fmt::Display for RedBEventLog { fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> { write!(f,"RedBEventLog") } }
+
+/// The atomic commit protocol. We use serde_cbor to encode keys as bytes before writing them through redb tables — this avoids having to implement Key/Value traits for every tuple variant we put in storage, keeping the impl minimal and testable without pulling redb's more exotic features into tests.
+#[async_trait]
+impl crate::eventlog::EventLog for RedBEventLog {