feat(timezone): add timezone-aware session context (#671)

* feat(timezone): add timezone-aware session context (#661)

All timestamps were UTC-only, causing daily logs to split at UTC midnight,
cron schedules to fire in UTC, and no quiet hours for heartbeat. This adds
timezone as a per-session property flowing from the client.

Key changes:
- New `src/timezone.rs` module with resolution chain, parsing, and detection
- `IncomingMessage` carries optional timezone from client
- `JobContext.user_timezone` flows timezone to tools
- `next_cron_fire()` accepts timezone for schedule evaluation
- `Trigger::Cron` stores optional timezone (backward-compatible)
- Workspace gains `_tz` variants for daily logs and system prompt
- Heartbeat supports quiet hours (`HEARTBEAT_QUIET_START/END`)
- Web frontend sends `Intl.DateTimeFormat().resolvedOptions().timeZone`
- REPL auto-detects system timezone
- `DEFAULT_TIMEZONE` env var / settings for server-wide default

Storage stays UTC. Conversion happens at display boundaries.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix(timezone): address review feedback on timezone-aware sessions

- Validate quiet hours values (0-23) in HeartbeatConfig::resolve()
- Fall back to settings values when env vars are unset for quiet hours
- Validate IANA timezone strings in routine_create/update with parse_timezone
- Add timezone field to routine_create tool schema
- Allow standalone timezone update on cron routines without changing schedule
- Return path from append_daily_log_tz to avoid TOCTOU race at midnight
- Delegate append_daily_log to append_daily_log_tz(entry, UTC) to avoid drift
- Preserve timezone through approval flow via PendingApproval.user_timezone
- Improve test_today_in_tz to not depend on hardcoded year
- Add 3 regression tests for quiet hours config validation

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* style: fix formatting in routine.rs

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix(timezone): address second round of review feedback

- Remove .claude/scheduled_tasks.lock from repo and add to .gitignore
- Store resolved timezone (not raw message.timezone) in PendingApproval
- Carry forward user_timezone through chained approvals in thread_ops
- Wire quiet_hours_start/end from config to HeartbeatRunner
- Support X-Timezone header as fallback in chat_send_handler

[skip-regression-check]

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix(timezone): include user's local time in time tool response

The time tool's "now" operation now returns local_iso and timezone
fields based on ctx.user_timezone, so the LLM can report time in
the user's timezone instead of always UTC.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* style: fix formatting in time.rs

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix(timezone): address Copilot review round 3 — validation, deterministic tests, schema fixes

- Validate DEFAULT_TIMEZONE and HEARTBEAT_TIMEZONE at config load time
- Add timezone field to HeartbeatSettings and config::HeartbeatConfig
- Wire heartbeat timezone from config through agent_loop to HeartbeatRunner
- Add timezone to routine_update tool schema (was accepted but not advertised)
- Error on schedule/timezone update for non-cron routines
- Validate timezone in Trigger::from_db (coerce invalid to None with warning)
- Validate timezone in approval path (thread_ops.rs) before overwriting
- Time tool always includes timezone/local_iso fields (fallback to UTC)
- Make quiet hours tests deterministic using current UTC hour
- Add regression tests for config validation

[skip-regression-check]

Co-Authored-By: Claude Opus 4.6 <[email protected]>

---------

Co-authored-by: Claude Opus 4.6 <[email protected]>

src/settings.rs

@@ -291,6 +291,18 @@ pub struct HeartbeatSettings {
     /// User ID to notify on heartbeat findings.
     #[serde(default)]
     pub notify_user: Option<String>,
+
+    /// Hour (0-23) when quiet hours start (heartbeat skipped).
+    #[serde(default)]
+    pub quiet_hours_start: Option<u32>,
+
+    /// Hour (0-23) when quiet hours end (heartbeat resumes).
+    #[serde(default)]
+    pub quiet_hours_end: Option<u32>,
+
+    /// Timezone for quiet hours evaluation (IANA name, e.g. "America/New_York").
+    #[serde(default)]
+    pub timezone: Option<String>,
 }
 
 fn default_heartbeat_interval() -> u64 {
@@ -304,6 +316,9 @@ impl Default for HeartbeatSettings {
             interval_secs: default_heartbeat_interval(),
             notify_channel: None,
             notify_user: None,
+            quiet_hours_start: None,
+            quiet_hours_end: None,
+            timezone: None,
         }
     }
 }
@@ -351,6 +366,10 @@ pub struct AgentSettings {
     /// When true, skip tool approval checks entirely. For benchmarks/CI.
     #[serde(default)]
     pub auto_approve_tools: bool,
+
+    /// Default timezone for new sessions (IANA name, e.g. "America/New_York").
+    #[serde(default = "default_timezone")]
+    pub default_timezone: String,
 }
 
 fn default_agent_name() -> String {
@@ -385,6 +404,10 @@ fn default_max_tool_iterations() -> usize {
     50
 }
 
+fn default_timezone() -> String {
+    "UTC".to_string()
+}
+
 fn default_true() -> bool {
     true
 }
@@ -402,6 +425,7 @@ impl Default for AgentSettings {
             session_idle_timeout_secs: default_session_idle_timeout(),
             max_tool_iterations: default_max_tool_iterations(),
             auto_approve_tools: false,
+            default_timezone: default_timezone(),
         }
     }
 }