Add the session store: baseline file and append-only log

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

docs/implementer-log.md

@@ -34,6 +34,7 @@ reviewer adds findings under "Reviews" once per milestone.
 | M2b/02-loopd-config | 2026-09-18 | done | 2 | fail | none | Added Paths/Channel/Loop/Baseline structs to config.rs with `#[serde(deny_unknown_fields, default)]` and Debug/Clone/PartialEq/Eq/Deserialize (Default derived for Channel, hand-written for the other three: home is $BOXMAKER_HOME else /var/lib/boxmaker, loop is 8/true/16384, baseline system is system.md); Config gained the four `#[serde(default)]` fields and `channel_socket()` fills the default `<home>/run/loop/loop.sock` when the socket is empty. `load` joins `baseline.system` to the config file's directory via `parent.join` (which replaces an already-absolute path); `parse` leaves it. 9 config tests pass, `deny_unknown_fields` count is 10. Two clippy fixes on the first (failing) gate run: the nested if in `load` collapsed by relying on Path::join replacing absolute paths instead of a 1.98 let-chain, and `Path::is_empty` (stable 1.98) replaced with `as_os_str().is_empty()`. | ? |
 | M2b/03-loopd-tools | 2026-09-18 | done | 1 | pass | none | Added `pub mod tools;` to lib.rs and `serde::Serialize`/`serde::Deserialize`/`deny_unknown_fields` to ToolSchema; wrote crates/loopd/src/tools.rs with ToolPort, Entry, Registry (m2b/config), core_schemas/get/find, FIND_TOOL/CALL_TOOL constants, clock_schema/echo_schema, Dispatch with dispatch (find_tool/call_tool/local dispatch rows), cap_result via floor_char_boundary, and FakeTools recording calls and answering clock/echo/denying others with `unwrap_or_else(|p| p.into_inner())` on Mutex::lock. 7 tools tests pass, `make gate` prints `gate: ok`, no `unwrap()` in tools.rs. | ? |
 | M2b/04-loopd-baseline | 2026-09-18 | done | 2 | fail | none | Wrote crates/loopd/src/baseline.rs: `Baseline` (system prompt + core tool schemas, `deny_unknown_fields`), `BaselineError` (Read/Parse name the file, plus Hash) with Display/std::error::Error, `assemble` (system prompt trimmed of trailing whitespace, core memory appended with a blank line when its trimmed content is non-empty), `to_json`/`from_json`, `load`, and `hash` (sha256 of the canonical JSON). `messages` prepends the system message and replays every `LogRecord` variant explicitly named, so a new one is a compile error. The `\n\n` separator between system prompt and core memory had to be two newlines (a blank line), not one. All 6 baseline tests pass and all loopd tests pass with the new support module; first gate run failed on a rustfmt import-order diff, fixed with `cargo fmt`. | ? |
+| M2b/05-loopd-session | 2026-09-18 | done | 2 | fail | none | Copied the given test byte-identical and wrote crates/loopd/src/session.rs: `Session` (id, dir, baseline, records, appended log file, next_call) and `SessionError` (Exists/NotFound/Io/Torn/Baseline/Encode) with derived Debug, Display and std::error::Error::source. `create` refuses an existing dir, writes `0.baseline.json`, opens `0.jsonl` with `create_new`+`append`, and appends a `SessionStart` (`Timestamp::now()`, epoch 0, the slot, `baseline.hash()`). `open` reads the baseline from the file (not `system.md`), requires every log line to end in `\n` and parse as a `LogRecord` else `Torn` with the 1-based line and reason, and sets `next_call` to one past the highest `ToolResult` call. `append` encodes, writes, `sync_data()`, then pushes to memory. All 7 session tests pass. First gate failed on clippy: split the `source()` arm that bound three different error types into three arms, removed the redundant `.write(true)` (implied by `append`), and used `path.display()` for the `Torn` path. | ? |
 
 
 ## Reviews