chore(conductor): Add new track 'Generic RRULE Formatter'

conductor/tracks.md

@@ -21,3 +21,8 @@ This file tracks all major tracks for the project. Each track has its own detail
 
 - [x] **Track: Fix RRULE UNTIL object conversion error: Invalid UNTIL value: [object Object]**
   *Link: [./tracks/fix_rrule_until_conversion_20260219/](./tracks/fix_rrule_until_conversion_20260219/)*
+
+---
+
+- [ ] **Track: Fix SyntaxError: Invalid weekday string: [object Object] by implementing a generic recursive RRULE formatter.**
+  *Link: [./tracks/rrule_generic_formatter_20260219/](./tracks/rrule_generic_formatter_20260219/)*

conductor/tracks/rrule_generic_formatter_20260219/index.md

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+# Track rrule_generic_formatter_20260219 Context
+
+- [Specification](./spec.md)
+- [Implementation Plan](./plan.md)
+- [Metadata](./metadata.json)

conductor/tracks/rrule_generic_formatter_20260219/metadata.json

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+{
+  "track_id": "rrule_generic_formatter_20260219",
+  "type": "bug",
+  "status": "new",
+  "created_at": "2026-02-19T00:00:00Z",
+  "updated_at": "2026-02-19T00:00:00Z",
+  "description": "Fix SyntaxError: Invalid weekday string: [object Object] by implementing a generic recursive RRULE formatter."
+}

conductor/tracks/rrule_generic_formatter_20260219/plan.md

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+# Implementation Plan - Generic RRULE Formatter
+
+## Phase 1: Reproduction & Test Setup
+- [ ] Task: Create reproduction test case for `BYDAY` object
+    - [ ] Add a test in `icalendar_test.ts` mocking a `BYDAY` property as an array of objects (e.g. `[{ day: 'MO' }]`).
+    - [ ] Run the test and confirm it fails with `SyntaxError: Invalid weekday string: [object Object]`.
+- [ ] Task: Conductor - User Manual Verification 'Reproduction & Test Setup' (Protocol in workflow.md)
+
+## Phase 2: Implementation
+- [ ] Task: Implement Recursive Formatter
+    - [ ] Update `formatRRuleValue` in `icalendar.ts` to be a recursive function.
+    - [ ] Handle Arrays by joining elements with commas.
+    - [ ] Handle `Date` objects using the existing iCal format.
+    - [ ] Handle property objects (extract `date`, `day`, or `value` properties).
+    - [ ] Run the reproduction test to confirm it passes.
+- [ ] Task: Conductor - User Manual Verification 'Implementation' (Protocol in workflow.md)
+
+## Phase 3: Verification & Cleanup
+- [ ] Task: Composite and Regression Testing
+    - [ ] Add a complex test case containing both nested `UNTIL` dates and `BYDAY` arrays.
+    - [ ] Run the full regression test suite in `icalendar_test.ts`.
+- [ ] Task: Conductor - User Manual Verification 'Verification & Cleanup' (Protocol in workflow.md)

conductor/tracks/rrule_generic_formatter_20260219/spec.md

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+# Specification: Generic RRULE Object Formatter
+
+## Overview
+The current implementation for converting RRULE objects (from `ts-ics`) back to strings is brittle and fails when encountering nested objects or arrays for properties like `BYDAY`. This results in `[object Object]` being injected into the RRULE string, causing syntax errors in the `rrule` library. This track replaces the specific property handling with a robust, recursive generic formatter.
+
+## Functional Requirements
+- **Recursive Value Formatting:** The `formatRRuleValue` function must handle nested structures:
+    - **Arrays:** Join elements with commas (e.g., `['MO', 'TU']` -> `MO,TU`).
+    - **Date Objects:** Format as `YYYYMMDDTHHMMSSZ`.
+    - **Nested Property Objects:** If an object has a `date`, `day`, or `value` property, extract and format that value (e.g., `{ day: 'MO' }` -> `MO`).
+    - **Recursion:** If an array contains objects, or an object contains an array, the logic must recurse until primitives are reached.
+- iCalendar Compliance: Ensure the resulting string for every property matches the iCalendar spec format expected by `rrule.js`.
+
+## Implementation Steps
+1. Reproduce: Create a test case in `icalendar_test.ts` where `BYDAY` is an object or an array of objects. Verify it fails with `Invalid weekday string: [object Object]`.
+2. Fix: Re-implement `formatRRuleValue` in `icalendar.ts` as a recursive function that handles Arrays, Dates, and standard `ts-ics` nested value objects.
+3. Verify: 
+    - Confirm the `BYDAY` reproduction test passes.
+    - Add a composite test with `UNTIL` (Date) and `BYDAY` (Array) together.
+    - Run regression tests to ensure standard string RRULEs still work.
+
+## Acceptance Criteria
+- [ ] `expandRecurrences` correctly handles `BYDAY` when provided as an array of objects.
+- [ ] `expandRecurrences` correctly handles `UNTIL` when provided as a nested date object.
+- [ ] All 12+ existing tests pass, including regression checks for string-based RRULEs.