120 no std aimx server dispatch port cross cutting anyrecord recordmetadatatracker de std

[lxsaah]

no_std AimX server (dispatch) port — cross-cutting AnyRecord + RecordMetadataTracker de-std

Closes #120. Follow-up to #39 / design doc 041.

What this does

The Phase 6 foundation (#39) landed the generic session connectors, the aimdb-uds-connector crate, and a no_std AimX codec — i.e. the embedded client path (a sensor dialing a gateway). What stayed std-only was the AimX server dispatch (AimxDispatch/AimxSession).

This PR lifts that dispatch — and the central record API it reaches into — onto no_std + alloc, so an MCU can now serve a host (e.g. "board answers a host over serial": record.list / get / set / drain / subscribe), not just dial one.

Tracing the dependency to the bottom, this is a cross-cutting refactor of core's record API, not a mechanical re-gate.

Approach: a dedicated remote-access feature

Rather than overload json-serialize, the server data model now sits behind a new feature:

remote-access = ["json-serialize", "thiserror"]   # transitively enabled by `std`

This cleanly separates the two embedded opt-ins:

Feature	Gives you	Path
json-serialize	JSON value codec — record.latest()?.as_json()	embedded client
remote-access	record metadata + introspection, the type-erased JSON read/write/subscribe API, the wire protocol/config/security/error types, and the AimX server dispatch (with connector-session)	embedded server

std pulls in remote-access transitively, so std builds are unaffected.

Changes by area

aimdb-core — the cross-cutting de-std

• Re-gated std → remote-access: the AnyRecord trait methods (collect_metadata / latest_json / subscribe_json / set_from_json), the JsonBufferReader trait, the remote module, and the AimDb/AimDbInner JSON API (list_records / try_latest_as_json / set_record_from_json).
• De-std'd the dispatch: std::collections::HashMap/HashSet → hashbrown, std::sync::Arc → alloc::sync::Arc.
• De-std'd the remote module: AimxConfig.socket_path PathBuf → String, SecurityPolicy HashSet → hashbrown, thiserror pulled with default-features = false, From<std::io::Error> for RemoteError kept behind a std cfg.
• Removed RecordMetadataTracker (an Arc<Mutex<…>> + Arc<AtomicBool> + SystemTime::now() on every produce()). The surviving writable bit is now a single portable_atomic::AtomicBool field on TypedRecord; collect_metadata reads the type name + flag directly with no shared state.
• DbError::{runtime_error, permission_denied, record_key_not_found} pub(crate) constructors — let the JSON/remote paths write one error expression across std (message carried) and no_std (unit placeholder), replacing the inline #[cfg] splits.
• graph serde derives (RecordOrigin / GraphNode / GraphEdge / EdgeType) moved from the std gate to the serde feature (always on with alloc) so RecordMetadata serializes on no_std.

Runtime-neutral wall clock

RecordMetadataTracker tracked created_at / last_update via SystemTime — which has no no_std equivalent. Introduced an abstraction on the runtime adapter instead:

• aimdb-executor: new TimeOps::unix_time(&self) -> Option<(u64, u32)> — absolute wall-clock time, distinct from the monotonic now(). Default impl returns None (a bare MCU with no RTC).
• aimdb-tokio-adapter: implements it from the OS clock (SystemTime::now()).
• aimdb-embassy-adapter: EmbassyAdapter::set_unix_time(now_unix_secs) anchors a process-global u32 (Unix seconds at boot); unix_time() then derives (secs, nanos) from monotonic uptime + the anchor, returning None until the device learns the real time (NTP / GPS / host handshake).

aimdb-uds-connector

• UdsServer::new / socket_path take impl Into<String> (was impl Into<PathBuf>); the internal bind goes through std::path::Path::new(&socket_path) — same synchronous remove-stale → bind → set_permissions behavior.

Verification target (Makefile test-embedded)

Added the full no_std server cross-check, plus remote-access test/clippy lines:

cargo check --package aimdb-core --target thumbv7em-none-eabihf \
  --no-default-features --features "alloc,connector-session,remote-access"

Note: this differs from the literal command in #120, which used json-serialize. Under the new feature layout that builds only the codec — the dispatch is gated on remote-access. The Makefile uses the correct feature set.

Tooling fallout

• aimdb-mcp: list_records, the records resource, and query_schema no longer emit created_at / last_update (core stopped tracking them).
• aimdb-cli / aimdb-client: test fixtures updated for the RecordMetadata::new signature and the socket_path: String change (test-only).

Breaking changes

• RecordMetadata loses created_at / last_update; RecordMetadata::new drops its created_at parameter; with_last_update / with_last_update_opt removed. AimX record.list (and MCP / CLI output derived from it) no longer carry those two fields.
• AimxConfig.socket_path is now String (was PathBuf); AimxConfig::socket_path(...) / UdsServer::new(...) take impl Into<String>. &str / String callers are unaffected; &Path / PathBuf callers must convert (e.g. path.to_str().unwrap()).

Verification

All green:

• cargo check -p aimdb-core --no-default-features --features "alloc,remote-access" (host)
• cargo check -p aimdb-core --no-default-features --features "alloc,connector-session,remote-access" --target thumbv7em-none-eabihf — the AimX dispatch cross-compiles (the issue's target)
• cargo check -p aimdb-core --features "std,tracing,metrics"
• cargo check -p aimdb-embassy-adapter --target thumbv7em-none-eabihf
• cargo test -p aimdb-core --no-default-features --features "alloc,remote-access" — 7 passed
• cargo test -p aimdb-core --lib --features "std" remote:: — 18 passed
• No dangling references to the removed RecordMetadataTracker / created_at / last_update across either workspace; aimdb-pro's demo .socket_path("…") still compiles (&str: Into<String>).

Checklist (from #120)

• Re-gate the AnyRecord JSON + metadata methods off the std gate
• De-std RecordMetadataTracker (removed entirely; timestamp tracking dropped, writable → portable_atomic::AtomicBool)
• De-std the remote module (socket_path → String, HashSet → hashbrown, gate thiserror / io::Error)
• Re-gate the AimDb JSON API off std
• Re-gate AimxDispatch/AimxSession to connector-session + remote-access; std::collections → hashbrown, std::sync::Arc → alloc::sync::Arc
• Add the embedded dispatch check to the Makefile test-embedded target

Out of scope (separate follow-ups, per doc 041)

aimdb-serial-connector, aimdb-tcp-connector, host client AimxConnection::connect_over / connect_url, and the cli/mcp --connect <url> / AIMDB_CONNECT resolver.