diff --git a/server/src/service/common/item_id.rs b/server/src/service/common/item_id.rs
new file mode 100644
index 00000000..fe5f3ae4
--- /dev/null
+++ b/server/src/service/common/item_id.rs
@@ -0,0 +1,70 @@
+//! Pure helpers for pipeline item ID parsing.
+//!
+//! Pipeline item IDs share the format `{number}_{type}_{slug}`, e.g.
+//! `"42_story_foo"`, `"7_bug_bar"`, `"100_refactor_baz"`. The functions here
+//! extract or validate the leading numeric segment without performing any I/O.
+
+/// Extract the numeric prefix from a pipeline item ID.
+///
+/// Returns the leading digit sequence from IDs like `"42_story_foo"` → `"42"`.
+/// Returns `None` if the ID has no leading digit sequence.
+pub fn extract_item_number(item_id: &str) -> Option<&str> {
+    item_id
+        .split('_')
+        .next()
+        .filter(|s| !s.is_empty() && s.chars().all(|c| c.is_ascii_digit()))
+}
+
+#[allow(dead_code)]
+/// Return `true` if `item_id` has a valid `{digits}_` prefix format.
+///
+/// Valid: `"42_story_foo"`, `"1_bug_bar"`.
+/// Invalid: `"story_without_number"`, `""`, `"abc_story"`.
+pub fn has_valid_id_prefix(item_id: &str) -> bool {
+    extract_item_number(item_id).is_some()
+}
+
+// ── Tests ─────────────────────────────────────────────────────────────────────
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn extract_item_number_extracts_prefix() {
+        assert_eq!(extract_item_number("42_story_foo"), Some("42"));
+        assert_eq!(extract_item_number("1_bug_bar"), Some("1"));
+        assert_eq!(extract_item_number("100_refactor_baz"), Some("100"));
+        assert_eq!(
+            extract_item_number("261_story_bot_notifications"),
+            Some("261")
+        );
+        assert_eq!(extract_item_number("1_spike_research"), Some("1"));
+    }
+
+    #[test]
+    fn extract_item_number_returns_none_for_no_numeric_prefix() {
+        assert_eq!(extract_item_number("story_without_number"), None);
+        assert_eq!(extract_item_number("abc_story"), None);
+        assert_eq!(extract_item_number("abc_story_thing"), None);
+        assert_eq!(extract_item_number(""), None);
+    }
+
+    #[test]
+    fn extract_item_number_returns_none_for_empty_first_segment() {
+        // Leading underscore: first segment is "".
+        assert_eq!(extract_item_number("_story_thing"), None);
+    }
+
+    #[test]
+    fn has_valid_id_prefix_returns_true_for_valid_ids() {
+        assert!(has_valid_id_prefix("42_story_foo"));
+        assert!(has_valid_id_prefix("1_bug_bar"));
+    }
+
+    #[test]
+    fn has_valid_id_prefix_returns_false_for_invalid_ids() {
+        assert!(!has_valid_id_prefix("story_no_number"));
+        assert!(!has_valid_id_prefix(""));
+    }
+}
diff --git a/server/src/service/common/mod.rs b/server/src/service/common/mod.rs
new file mode 100644
index 00000000..8595a336
--- /dev/null
+++ b/server/src/service/common/mod.rs
@@ -0,0 +1,6 @@
+//! Shared pure helpers used by multiple service modules.
+//!
+//! All sub-modules here are pure (no I/O, no side effects). Any helper that
+//! duplicates logic across two or more service modules belongs here; anything
+//! used by only one service stays in that service.
+pub mod item_id;
diff --git a/server/src/service/mod.rs b/server/src/service/mod.rs
index 5acbb5d9..3397e5d8 100644
--- a/server/src/service/mod.rs
+++ b/server/src/service/mod.rs
@@ -8,6 +8,7 @@
 pub mod agents;
 pub mod anthropic;
 pub mod bot_command;
+pub mod common;
 pub mod diagnostics;
 pub mod events;
 pub mod file_io;
diff --git a/server/src/service/notifications/format.rs b/server/src/service/notifications/format.rs
index 43ef4a8f..d87887dc 100644
--- a/server/src/service/notifications/format.rs
+++ b/server/src/service/notifications/format.rs
@@ -4,6 +4,8 @@
 //! or borrowed string data.  They return `(plain_text, html)` pairs suitable
 //! for `ChatTransport::send_message`.
 
+use crate::service::common::item_id::extract_item_number;
+
 /// Human-readable display name for a pipeline stage directory.
 pub fn stage_display_name(stage: &str) -> &'static str {
     match stage {
@@ -17,14 +19,6 @@ pub fn stage_display_name(stage: &str) -> &'static str {
     }
 }
 
-/// Extract the numeric story number from an item ID like `"261_story_slug"`.
-pub fn extract_story_number(item_id: &str) -> Option<&str> {
-    item_id
-        .split('_')
-        .next()
-        .filter(|s| !s.is_empty() && s.chars().all(|c| c.is_ascii_digit()))
-}
-
 /// Format a stage transition notification message.
 ///
 /// Returns `(plain_text, html)` suitable for `ChatTransport::send_message`.
@@ -34,7 +28,7 @@ pub fn format_stage_notification(
     from_stage: &str,
     to_stage: &str,
 ) -> (String, String) {
-    let number = extract_story_number(item_id).unwrap_or(item_id);
+    let number = extract_item_number(item_id).unwrap_or(item_id);
     let name = story_name.unwrap_or(item_id);
 
     let prefix = if to_stage == "Done" { "\u{1f389} " } else { "" };
@@ -53,7 +47,7 @@ pub fn format_error_notification(
     story_name: Option<&str>,
     reason: &str,
 ) -> (String, String) {
-    let number = extract_story_number(item_id).unwrap_or(item_id);
+    let number = extract_item_number(item_id).unwrap_or(item_id);
     let name = story_name.unwrap_or(item_id);
 
     let plain = format!("\u{274c} #{number} {name} \u{2014} {reason}");
@@ -69,7 +63,7 @@ pub fn format_blocked_notification(
     story_name: Option<&str>,
     reason: &str,
 ) -> (String, String) {
-    let number = extract_story_number(item_id).unwrap_or(item_id);
+    let number = extract_item_number(item_id).unwrap_or(item_id);
     let name = story_name.unwrap_or(item_id);
 
     let plain = format!("\u{1f6ab} #{number} {name} \u{2014} BLOCKED: {reason}");
@@ -86,7 +80,7 @@ pub fn format_rate_limit_notification(
     story_name: Option<&str>,
     agent_name: &str,
 ) -> (String, String) {
-    let number = extract_story_number(item_id).unwrap_or(item_id);
+    let number = extract_item_number(item_id).unwrap_or(item_id);
     let name = story_name.unwrap_or(item_id);
 
     let plain =
@@ -121,30 +115,6 @@ mod tests {
         assert_eq!(stage_display_name(""), "Unknown");
     }
 
-    // ── extract_story_number ──────────────────────────────────────────────────
-
-    #[test]
-    fn extract_story_number_parses_numeric_prefix() {
-        assert_eq!(
-            extract_story_number("261_story_bot_notifications"),
-            Some("261")
-        );
-        assert_eq!(extract_story_number("42_bug_fix_thing"), Some("42"));
-        assert_eq!(extract_story_number("1_spike_research"), Some("1"));
-    }
-
-    #[test]
-    fn extract_story_number_returns_none_for_non_numeric() {
-        assert_eq!(extract_story_number("abc_story_thing"), None);
-        assert_eq!(extract_story_number(""), None);
-    }
-
-    #[test]
-    fn extract_story_number_returns_none_for_empty_first_segment() {
-        // Leading underscore: first segment is ""
-        assert_eq!(extract_story_number("_story_thing"), None);
-    }
-
     // ── format_stage_notification ─────────────────────────────────────────────
 
     #[test]
diff --git a/server/src/service/story/lifecycle.rs b/server/src/service/story/lifecycle.rs
index 89a272ac..5d286988 100644
--- a/server/src/service/story/lifecycle.rs
+++ b/server/src/service/story/lifecycle.rs
@@ -3,26 +3,9 @@
 //! These functions reason about story IDs and dependencies without performing
 //! any I/O. They inform routing decisions in `mod.rs` and the MCP adapter.
 
-#[allow(dead_code)]
-/// Extract the numeric prefix from a story ID (e.g. `"42"` from `"42_story_foo"`).
-///
-/// Returns `None` if the ID has no leading digit sequence.
-pub fn story_number(story_id: &str) -> Option<&str> {
-    let num = story_id.split('_').next()?;
-    if num.is_empty() || !num.chars().all(|c| c.is_ascii_digit()) {
-        return None;
-    }
-    Some(num)
-}
-
-#[allow(dead_code)]
-/// Return `true` if `story_id` has a valid `{digits}_` prefix format.
-///
-/// Valid: `"42_story_foo"`, `"1_bug_bar"`.
-/// Invalid: `"story_without_number"`, `""`, `"abc_story"`.
-pub fn has_valid_id_prefix(story_id: &str) -> bool {
-    story_number(story_id).is_some()
-}
+pub use crate::service::common::item_id::{
+    extract_item_number as story_number, has_valid_id_prefix,
+};
 
 // ── Tests ─────────────────────────────────────────────────────────────────────