Core error taxonomy + name validation (ADR-008 §4/§5, ADR-017 §3); AGENTS.md updated to Phase 1 posture

tasks/core-errors-and-validation.md

@@ -1,7 +1,7 @@
 ---
 id: core-errors-and-validation
 name: Core error taxonomy and name validation
-status: pending
+status: completed
 depends_on: [scaffold-workspace]
 scope: narrow
 risk: low
@@ -65,8 +65,59 @@ engine and the contract suite reference the same constant.
 
 ## Notes
 
-> To be filled by implementation agent
+- `thiserror` v2 added to `alkstore` — the crate's first (and, until
+  wave 2's serde work, only) dependency.
+- `Error::Database` carries
+  `#[source] Box<dyn std::error::Error + Send + Sync>` — the opaque
+  engine-detail carrier per ADR-008 §5. The `#[error(...)]` text is
+  deliberately terse ("database error") so it doesn't shadow the
+  source chain's detail. An `Error::database(err)` convenience
+  constructor wraps anything `Into<Box<dyn Error + Send + Sync>>`.
+- `Error::PayloadTooLarge { limit: usize }` — the limit is `usize`
+  (a byte count, not a std::io::ErrorKind-style re-export); doc text
+  carries the ADR-020 §4 serialization-quantity pin and the
+  pg-only/never-SQLite asymmetry.
+- Validation helpers split by name class exactly per ADR-008 §4's
+  third-round annotation: `validate_shared_name` (six shared kinds —
+  non-empty + reserved-prefix rejection) and `validate_local_name`
+  (stream-consumer names, `try_lock` owner, `worker_id` — non-empty
+  only). `NameKind::Shared`/`NameKind::Local` + `validate_name(kind,
+  name)` is the underlying pair; the two named helpers are the
+  ergonomic surface. Whitespace-only names are rejected as
+  `InvalidName` for both kinds (never a meaningful name on any
+  engine); names are not trimmed (the caller's name is stored as
+  given — engine quoting is the engine's obligation).
+- The reserved-string test asserts its shared-name rejection carries
+  `ReservedName` (it carries the reserved prefix, so it can never be
+  a legal *shared* name) while `validate_local_name` accepts it — the
+  two name classes distinguished in tests, mirroring the ADR text.
+- `#[non_exhaustive]` was verified on the enum definition, not in
+  this crate's tests: in-crate matching stays exhaustive (the
+  mechanical catch-all enforcement binds downstream crates, per the
+  Rust rules ADR-017 §3 relies on) — a test here asserting a
+  necessary wildcard is unreachable-code, flagged clippy `warn(unreachable_patterns)`.
+- `schedule()`/`run_schedules`' `InvalidSpec`/`LeadershipLost`
+  variants (core-contract §Errors, ADR-009 §6) are *not* minted here
+  — the six-variant list is this task's exact scope; the scheduler
+  variants land with the trait-surface task that pins their
+  signatures.
 
 ## Summary
 
-> To be filled on completion
+Core error taxonomy and name validation implemented in `alkstore`.
+`src/error.rs`: `Error` — exactly the six v1 variants
+(`PayloadTooLarge { limit }`, `ReservedName { name }`,
+`InvalidName { name }`, `Closed`, `Codec(String)`, `Database`
+with `#[source]`), `thiserror`-derived, `#[non_exhaustive]`, plus
+the `Result<T>` alias (the prelude shape downstream crates use).
+`src/validation.rs`: `RESERVED_PREFIX = "__alkstore_"`,
+`RESERVED_LISTENER_RECONNECTED =
+"__alkstore_listener_reconnected__"` (public for the pg engine and
+contract suite), `NameKind::{Shared, Local}`, and
+`validate_shared_name`/`validate_local_name`/`validate_name`
+helpers. All types re-exported from `src/lib.rs`. Ten unit tests
+cover empty/whitespace-only/reserved-prefix/reserved-string/legal
+names for both classes and the error display/source behavior.
+`cargo test -p alkstore` (10 pass), `cargo clippy
+--all-targets -- -D warnings`, and `cargo fmt --check` all clean;
+workspace `cargo build` compiles all three crates.