Keep latest-session timestamps increasing under tight loops

The next repo-local sweep target was ROADMAP ultraworkers#73: repeated backlog
sweeps exposed that session writes could share the same wall-clock
millisecond, which made semantic recency fragile and forced the
resume-latest regression to sleep between saves. The fix makes session
timestamps monotonic within the process and removes the timing hack
from the test so latest-session selection stays stable under tight
loops.

Constraint: Preserve the existing session file format while changing only the timestamp source semantics
Rejected: Keep the sleep-based test workaround | hides the real ordering hazard instead of fixing timestamp generation
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: Any future session-recency logic must keep `current_time_millis`, ordering tests, and latest-session expectations aligned
Tested: cargo fmt --all --check; cargo clippy --workspace --all-targets -- -D warnings; cargo test --workspace; architect review APPROVE
Not-tested: Cross-process monotonicity when multiple binaries write sessions concurrently

Author: Yeachan-Heo

ROADMAP.md

@@ -517,3 +517,4 @@ Model name prefix now wins unconditionally over env-var presence. Regression tes
 71. **Wrong-task prompt receipt is not detected before execution** — **done (verified 2026-04-12):** worker boot prompt dispatch now accepts an optional structured `task_receipt` (`repo`, `task_kind`, `source_surface`, `expected_artifacts`, `objective_preview`) and treats mismatched visible prompt context as a `WrongTask` prompt-delivery failure before execution continues. The prompt-delivery payload now records `observed_prompt_preview` plus the expected receipt, and regression coverage locks both the existing shell/wrong-target paths and the new KakaoTalk-style wrong-task mismatch case. **Original filing below.**
 
 72. **`latest` managed-session selection depends on filesystem mtime before semantic session recency** — **done (verified 2026-04-12):** managed-session summaries now carry `updated_at_ms`, `SessionStore::list_sessions()` sorts by semantic recency before filesystem mtime, and regression coverage locks the case where `latest` must prefer the newer session payload even when file mtimes point the other way. The CLI session-summary wrapper now stays in sync with the runtime field so `latest` resolution uses the same ordering signal everywhere. **Original filing below.**
+73. **Session timestamps are not monotonic enough for latest-session ordering under tight loops** — **done (verified 2026-04-12):** runtime session timestamps now use a process-local monotonic millisecond source, so back-to-back saves still produce increasing `updated_at_ms` even when the wall clock does not advance. The temporary sleep hack was removed from the resume-latest regression, and fresh workspace verification stayed green with the semantic-recency ordering path from #72. **Original filing below.**

rust/crates/runtime/src/session.rs

@@ -13,6 +13,7 @@ const SESSION_VERSION: u32 = 1;
 const ROTATE_AFTER_BYTES: u64 = 256 * 1024;
 const MAX_ROTATED_FILES: usize = 3;
 static SESSION_ID_COUNTER: AtomicU64 = AtomicU64::new(0);
+static LAST_TIMESTAMP_MS: AtomicU64 = AtomicU64::new(0);
 
 /// Speaker role associated with a persisted conversation message.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -1030,10 +1031,27 @@ fn normalize_optional_string(value: Option<String>) -> Option<String> {
 }
 
 fn current_time_millis() -> u64 {
-    SystemTime::now()
+    let wall_clock = SystemTime::now()
         .duration_since(UNIX_EPOCH)
         .map(|duration| u64::try_from(duration.as_millis()).unwrap_or(u64::MAX))
-        .unwrap_or_default()
+        .unwrap_or_default();
+
+    let mut candidate = wall_clock;
+    loop {
+        let previous = LAST_TIMESTAMP_MS.load(Ordering::Relaxed);
+        if candidate <= previous {
+            candidate = previous.saturating_add(1);
+        }
+        match LAST_TIMESTAMP_MS.compare_exchange(
+            previous,
+            candidate,
+            Ordering::SeqCst,
+            Ordering::SeqCst,
+        ) {
+            Ok(_) => return candidate,
+            Err(actual) => candidate = actual.saturating_add(1),
+        }
+    }
 }
 
 fn generate_session_id() -> String {
@@ -1125,15 +1143,25 @@ fn cleanup_rotated_logs(path: &Path) -> Result<(), SessionError> {
 #[cfg(test)]
 mod tests {
     use super::{
-        cleanup_rotated_logs, rotate_session_file_if_needed, ContentBlock, ConversationMessage,
-        MessageRole, Session, SessionFork,
+        cleanup_rotated_logs, current_time_millis, rotate_session_file_if_needed, ContentBlock,
+        ConversationMessage, MessageRole, Session, SessionFork,
     };
     use crate::json::JsonValue;
     use crate::usage::TokenUsage;
     use std::fs;
     use std::path::{Path, PathBuf};
     use std::time::{SystemTime, UNIX_EPOCH};
 
+    #[test]
+    fn session_timestamps_are_monotonic_under_tight_loops() {
+        let first = current_time_millis();
+        let second = current_time_millis();
+        let third = current_time_millis();
+
+        assert!(first < second);
+        assert!(second < third);
+    }
+
     #[test]
     fn persists_and_restores_session_jsonl() {
         let mut session = Session::new();

rust/crates/rusty-claude-cli/tests/resume_slash_commands.rs

@@ -3,8 +3,6 @@ use std::path::Path;
 use std::path::PathBuf;
 use std::process::{Command, Output};
 use std::sync::atomic::{AtomicU64, Ordering};
-use std::thread;
-use std::time::Duration;
 use std::time::{SystemTime, UNIX_EPOCH};
 
 use runtime::ContentBlock;
@@ -193,7 +191,6 @@ fn resume_latest_restores_the_most_recent_managed_session() {
     older
         .save_to_path(&older_path)
         .expect("older session should persist");
-    thread::sleep(Duration::from_millis(2));
 
     let mut newer = workspace_session(&project_dir).with_persistence_path(&newer_path);
     newer