diff --git a/conductor/tracks.md b/conductor/tracks.md
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--- a/conductor/tracks.md
+++ b/conductor/tracks.md
@@ -6,3 +6,8 @@ This file tracks all major tracks for the project. Each track has its own detail
 
 - [x] **Track: Upgrade the SilverBullet iCalendar plug to use DST-aware timezone resolution and add recurring event support using rrule.**
   *Link: [./tracks/timezone_rrule_20260218/](./tracks/timezone_rrule_20260218/)*
+
+---
+
+- [ ] **Track: Fix TypeError: r.replace is not a function in icalendar.ts**
+  *Link: [./tracks/fix_rrule_type_error_20260219/](./tracks/fix_rrule_type_error_20260219/)*
diff --git a/conductor/tracks/fix_rrule_type_error_20260219/index.md b/conductor/tracks/fix_rrule_type_error_20260219/index.md
new file mode 100644
index 0000000..73e78a1
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+++ b/conductor/tracks/fix_rrule_type_error_20260219/index.md
@@ -0,0 +1,5 @@
+# Track fix_rrule_type_error_20260219 Context
+
+- [Specification](./spec.md)
+- [Implementation Plan](./plan.md)
+- [Metadata](./metadata.json)
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diff --git a/conductor/tracks/fix_rrule_type_error_20260219/metadata.json b/conductor/tracks/fix_rrule_type_error_20260219/metadata.json
new file mode 100644
index 0000000..9def283
--- /dev/null
+++ b/conductor/tracks/fix_rrule_type_error_20260219/metadata.json
@@ -0,0 +1,8 @@
+{
+  "track_id": "fix_rrule_type_error_20260219",
+  "type": "bug",
+  "status": "new",
+  "created_at": "2026-02-19T00:00:00Z",
+  "updated_at": "2026-02-19T00:00:00Z",
+  "description": "Fix TypeError: r.replace is not a function in icalendar.ts"
+}
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diff --git a/conductor/tracks/fix_rrule_type_error_20260219/plan.md b/conductor/tracks/fix_rrule_type_error_20260219/plan.md
new file mode 100644
index 0000000..c146dfc
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+++ b/conductor/tracks/fix_rrule_type_error_20260219/plan.md
@@ -0,0 +1,20 @@
+# Implementation Plan - Fix `r.replace is not a function`
+
+## Phase 1: Reproduction & Test Setup
+- [ ] Task: Create a reproduction test case
+    - [ ] Create a new test case in `icalendar_test.ts` that mocks an event with a non-string `rrule` property (e.g., an object or number).
+    - [ ] Run the test to confirm it fails with the expected `TypeError`.
+- [ ] Task: Conductor - User Manual Verification 'Reproduction & Test Setup' (Protocol in workflow.md)
+
+## Phase 2: Implementation
+- [ ] Task: Implement defensive check in `icalendar.ts`
+    - [ ] Modify `expandRecurrences` function to check if `rruleStr` is a string before calling `.replace()`.
+    - [ ] If `rruleStr` is not a string, log a warning and return the original event (non-recurring fallback).
+    - [ ] Run the reproduction test again to confirm it passes.
+- [ ] Task: Conductor - User Manual Verification 'Implementation' (Protocol in workflow.md)
+
+## Phase 3: Verification & Cleanup
+- [ ] Task: Verify fix and check for regressions
+    - [ ] Run all tests in `icalendar_test.ts` to ensure existing functionality is preserved.
+    - [ ] (Optional) Verify with actual calendar sync if possible/safe.
+- [ ] Task: Conductor - User Manual Verification 'Verification & Cleanup' (Protocol in workflow.md)
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diff --git a/conductor/tracks/fix_rrule_type_error_20260219/spec.md b/conductor/tracks/fix_rrule_type_error_20260219/spec.md
new file mode 100644
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+++ b/conductor/tracks/fix_rrule_type_error_20260219/spec.md
@@ -0,0 +1,25 @@
+# Specification: Fix `r.replace is not a function` in `expandRecurrences`
+
+## Overview
+This track addresses a `TypeError: r.replace is not a function` error occurring in `icalendar.ts` during calendar synchronization. The error suggests that the `rrule` property of an event is not a string when it reaches the `expandRecurrences` function, causing the subsequent `.replace()` call to fail. This is likely due to the `ts-ics` parser returning a non-string value (e.g., an object or `undefined`) for the `rrule` property in certain scenarios (specifically observed with Outlook calendars).
+
+## Functional Requirements
+- **Defensive RRULE Handling:** The `expandRecurrences` function in `icalendar.ts` must safely handle cases where `rrule` (or `recurrenceRule`) is not a string.
+- **Graceful Fallback:** If `rrule` is not a string:
+    - It should be ignored/logged if it cannot be interpreted as a valid RRULE string, preventing the crash.
+    - The event should still be processed (treated as a non-recurring event if the rule is invalid), rather than crashing the entire sync for that event.
+
+## Non-Functional Requirements
+- **Stability:** The plug should not crash or throw unhandled exceptions during sync due to malformed or unexpected property types in the source ICS data.
+- **Logging:** Maintain existing error logging but ensure the error message is descriptive (e.g., "Invalid RRULE type: object").
+
+## Implementation Steps
+1.  **Reproduce Issue:** Create a unit test in `icalendar_test.ts` that mocks an `icsEvent` with a non-string `rrule` property (e.g., an object or number) and calls `expandRecurrences`.
+2.  **Implement Fix:** Modify `icalendar.ts` to check the type of `rruleStr` before calling `.replace()`.
+    - If it's not a string, attempt to convert it or return the original event (as if no recurrence rule exists) with a warning.
+3.  **Verify:** Run the new unit test to confirm the fix.
+
+## Acceptance Criteria
+- [ ] A new unit test case exists in `icalendar_test.ts` that passes with a non-string `rrule`.
+- [ ] The `expandRecurrences` function no longer throws `TypeError: r.replace is not a function` when `rrule` is not a string.
+- [ ] The sync process completes successfully even if some events have malformed `rrule` properties.
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