diff --git a/scripts/modules/task-manager/parse-prd/parse-prd-helpers.js b/scripts/modules/task-manager/parse-prd/parse-prd-helpers.js
index 565b229c..0668794f 100644
--- a/scripts/modules/task-manager/parse-prd/parse-prd-helpers.js
+++ b/scripts/modules/task-manager/parse-prd/parse-prd-helpers.js
@@ -120,19 +120,21 @@ export function validateFileOperations({
 }
 
 /**
- * Process and transform tasks with ID remapping
- * @param {Array} rawTasks - Raw tasks from AI
- * @param {number} startId - Starting ID for new tasks
- * @param {Array} existingTasks - Existing tasks for dependency validation
- * @param {string} defaultPriority - Default priority for tasks
- * @returns {Array} Processed tasks with remapped IDs
- */
+ * Transform raw PRD tasks into normalized tasks with reassigned sequential IDs.
+ * @param {Array} rawTasks - Tasks parsed from a PRD; each task must include an integer `id`.
+ * @param {number} startId - ID to assign to the first processed task.
+ * @param {Array} existingTasks - Existing tasks used to validate dependency references.
+ * @param {string} defaultPriority - Priority to apply when a task has no priority.
+ * @returns {Array} An array of tasks with reassigned sequential IDs, normalized fields (status, priority, title, description, details, testStrategy, subtasks), and dependencies remapped to the new IDs.
 export function processTasks(
 	rawTasks,
 	startId,
 	existingTasks,
 	defaultPriority
 ) {
+	// Runtime guard: ensure PRD task IDs are unique and sequential (1..N).
+	validateSequentialTaskIds(rawTasks, startId);
+
 	let currentId = startId;
 	const taskMap = new Map();
 
@@ -172,6 +174,54 @@ export function processTasks(
 	return processedTasks;
 }
 
+/**
+ * Validate that an array of PRD tasks uses unique, positive integer IDs that form a contiguous sequence.
+ *
+ * Validates that each task has an integer `id` >= 1, that IDs are unique, and that the sorted IDs form
+ * a contiguous sequence starting at either `1` or the provided `expectedStartId`.
+ *
+ * @param {Array<{id: number}>} rawTasks - Array of task objects containing an `id` property. If not an array or empty, no validation is performed.
+ * @param {number} [expectedStartId=1] - Allowed alternative starting ID for the contiguous sequence.
+ * @throws {Error} If any `id` is not an integer >= 1: "PRD tasks must use sequential positive integer IDs starting at 1."
+ * @throws {Error} If IDs are not unique: "PRD task IDs must be unique and sequential starting at 1."
+ * @throws {Error} If the sequence does not start at `1` or `expectedStartId`: "PRD task IDs must start at 1 or {expectedStartId} and be sequential."
+ * @throws {Error} If IDs are not contiguous: "PRD task IDs must be a contiguous sequence starting at {startId}."
+ */
+function validateSequentialTaskIds(rawTasks, expectedStartId = 1) {
+	if (!Array.isArray(rawTasks) || rawTasks.length === 0) {
+		return;
+	}
+
+	const ids = rawTasks.map((task) => task.id);
+
+	if (ids.some((id) => !Number.isInteger(id) || id < 1)) {
+		throw new Error(
+			'PRD tasks must use sequential positive integer IDs starting at 1.'
+		);
+	}
+
+	const uniqueIds = new Set(ids);
+	if (uniqueIds.size !== ids.length) {
+		throw new Error('PRD task IDs must be unique and sequential starting at 1.');
+	}
+
+	const sortedIds = [...uniqueIds].sort((a, b) => a - b);
+	const startId = sortedIds[0];
+	if (startId !== 1 && startId !== expectedStartId) {
+		throw new Error(
+			`PRD task IDs must start at 1 or ${expectedStartId} and be sequential.`
+		);
+	}
+
+	for (let index = 0; index < sortedIds.length; index += 1) {
+		if (sortedIds[index] !== startId + index) {
+			throw new Error(
+				`PRD task IDs must be a contiguous sequence starting at ${startId}.`
+			);
+		}
+	}
+}
+
 /**
  * Save tasks to file with tag support
  * @param {string} tasksPath - Path to save tasks
@@ -380,4 +430,4 @@ export function displayNonStreamingCliOutput({
 	if (aiServiceResponse?.telemetryData) {
 		displayAiUsageSummary(aiServiceResponse.telemetryData, 'cli');
 	}
-}
+}
\ No newline at end of file
diff --git a/scripts/modules/task-manager/scope-adjustment.js b/scripts/modules/task-manager/scope-adjustment.js
index 66c44c21..0951f1f0 100644
--- a/scripts/modules/task-manager/scope-adjustment.js
+++ b/scripts/modules/task-manager/scope-adjustment.js
@@ -157,14 +157,22 @@ function getCurrentComplexityScore(taskId, context) {
 }
 
 /**
- * Regenerates subtasks for a task based on new complexity while preserving completed work
- * @param {Object} task - The updated task object
- * @param {string} tasksPath - Path to tasks.json
- * @param {Object} context - Context containing projectRoot, tag, session
- * @param {string} direction - Direction of scope change (up/down) for logging
- * @param {string} strength - Strength level ('light', 'regular', 'heavy')
- * @param {number|null} originalComplexity - Original complexity score for smarter adjustments
- * @returns {Promise<Object>} Object with updated task and regeneration info
+ * Regenerates a task's pending subtasks to match a changed complexity while preserving subtasks with work already done.
+ *
+ * Generates new pending subtasks (via the configured AI service) to reach a target subtask count based on direction and strength, preserves subtasks whose status indicates work should be kept, and remaps IDs/dependencies so generated subtasks follow preserved ones.
+ *
+ * @param {Object} task - The task object to update; its subtasks array will be replaced with preserved and newly generated subtasks in the returned `updatedTask`.
+ * @param {string} tasksPath - Filesystem path to tasks.json (used for context; not modified by this function).
+ * @param {Object} context - Execution context containing { projectRoot, tag, session, ... } used for AI calls and logging.
+ * @param {string} direction - Scope change direction: 'up' to increase complexity or 'down' to decrease complexity.
+ * @param {string} [strength='regular'] - Adjustment strength: 'light', 'regular', or 'heavy'.
+ * @param {number|null} [originalComplexity=null] - Original complexity score (1-10) used to bias how aggressive the adjustment should be.
+ * @returns {Promise<Object>} An object with:
+ *   - updatedTask: the task object with preserved and regenerated subtasks,
+ *   - regenerated: `true` if new subtasks were generated, `false` otherwise,
+ *   - preserved: number of subtasks kept,
+ *   - generated: number of subtasks newly generated,
+ *   - error?: string when regeneration failed (present only on failure).
  */
 async function regenerateSubtasksForComplexity(
 	task,
@@ -378,6 +386,7 @@ Ensure the JSON is valid and properly formatted.`;
 		});
 
 		const generatedSubtasks = aiResult.mainResult.subtasks || [];
+		ensureSequentialSubtaskIds(generatedSubtasks);
 
 		// Post-process generated subtasks to ensure defaults
 		const processedGeneratedSubtasks = generatedSubtasks.map((subtask) => ({
@@ -441,6 +450,38 @@ Ensure the JSON is valid and properly formatted.`;
 	}
 }
 
+/**
+ * Validate that subtasks have unique, positive integer IDs forming a sequential series starting at 1.
+ *
+ * @param {Array<object>} subtasks - Array of subtask objects; each object is expected to have an `id` property.
+ * @throws {Error} If any `id` is not a positive integer ("Generated subtask ids must be positive integers").
+ * @throws {Error} If `id` values are not unique ("Generated subtasks must have unique ids").
+ * @throws {Error} If `id` values are not a contiguous sequence starting at 1 ("Generated subtask ids must be sequential starting from 1").
+ */
+function ensureSequentialSubtaskIds(subtasks) {
+	if (!Array.isArray(subtasks) || subtasks.length === 0) {
+		return;
+	}
+
+	const ids = subtasks.map((subtask) => subtask.id);
+	if (ids.some((id) => !Number.isInteger(id) || id < 1)) {
+		throw new Error('Generated subtask ids must be positive integers');
+	}
+	const uniqueIds = new Set(ids);
+	if (uniqueIds.size !== ids.length) {
+		throw new Error('Generated subtasks must have unique ids');
+	}
+
+	const sortedIds = [...uniqueIds].sort((a, b) => a - b);
+	for (let index = 0; index < sortedIds.length; index += 1) {
+		if (sortedIds[index] !== index + 1) {
+			throw new Error(
+				'Generated subtask ids must be sequential starting from 1'
+			);
+		}
+	}
+}
+
 /**
  * Generates AI prompt for scope adjustment
  * @param {Object} task - The task to adjust
@@ -872,4 +913,4 @@ export async function scopeDownTask(
 		updatedTasks,
 		telemetryData: combinedTelemetryData
 	};
-}
+}
\ No newline at end of file