diff --git a/packages/apps-engine/tests/server/accessors/SchedulerModify.spec.ts b/packages/apps-engine/tests/server/accessors/SchedulerModify.spec.ts
new file mode 100644
index 0000000000000..35926f55a92a9
--- /dev/null
+++ b/packages/apps-engine/tests/server/accessors/SchedulerModify.spec.ts
@@ -0,0 +1,137 @@
+import { AsyncTest, Expect, SetupFixture } from 'alsatian';
+
+import type { IOnetimeSchedule, IRecurringSchedule } from '../../../src/definition/scheduler';
+import { SchedulerModify } from '../../../src/server/accessors';
+import type { SchedulerBridge } from '../../../src/server/bridges';
+
+export class SchedulerModifyAccessorTestFixture {
+	private mockSchedulerBridge: SchedulerBridge;
+
+	private scheduleOnceCalls: Array<{ job: IOnetimeSchedule; appId: string }>;
+
+	private scheduleRecurringCalls: Array<{ job: IRecurringSchedule; appId: string }>;
+
+	private cancelJobCalls: Array<{ jobId: string; appId: string }>;
+
+	private cancelAllJobsCalls: string[];
+
+	@SetupFixture
+	public setupFixture(): void {
+		this.scheduleOnceCalls = [];
+		this.scheduleRecurringCalls = [];
+		this.cancelJobCalls = [];
+		this.cancelAllJobsCalls = [];
+
+		const { scheduleOnceCalls, scheduleRecurringCalls, cancelJobCalls, cancelAllJobsCalls } = this;
+
+		this.mockSchedulerBridge = {
+			doScheduleOnce(job: IOnetimeSchedule, appId: string): Promise<void> {
+				scheduleOnceCalls.push({ job, appId });
+				return Promise.resolve();
+			},
+			doScheduleRecurring(job: IRecurringSchedule, appId: string): Promise<void> {
+				scheduleRecurringCalls.push({ job, appId });
+				return Promise.resolve();
+			},
+			doCancelJob(jobId: string, appId: string): Promise<void> {
+				cancelJobCalls.push({ jobId, appId });
+				return Promise.resolve();
+			},
+			doCancelAllJobs(appId: string): Promise<void> {
+				cancelAllJobsCalls.push(appId);
+				return Promise.resolve();
+			},
+		} as SchedulerBridge;
+	}
+
+	@AsyncTest()
+	public async scheduleOnceAppendsAppIdWhenMissing(): Promise<void> {
+		const scheduler = new SchedulerModify(this.mockSchedulerBridge, 'test-app');
+		const job: IOnetimeSchedule = {
+			id: 'job-1',
+			when: new Date('2026-03-24T12:00:00.000Z'),
+			data: { pollId: '123' },
+		};
+
+		await Expect(() => scheduler.scheduleOnce(job)).not.toThrowAsync();
+
+		Expect(this.scheduleOnceCalls.length).toBe(1);
+		Expect(this.scheduleOnceCalls[0].appId).toBe('test-app');
+		Expect(this.scheduleOnceCalls[0].job).toEqual({
+			...job,
+			id: 'job-1_test-app',
+		});
+		Expect(job.id).toBe('job-1');
+	}
+
+	@AsyncTest()
+	public async scheduleOnceDoesNotAppendAppIdTwice(): Promise<void> {
+		const scheduler = new SchedulerModify(this.mockSchedulerBridge, 'test-app');
+		const job: IOnetimeSchedule = {
+			id: 'job-1_test-app',
+			when: 'in 5 minutes',
+		};
+
+		await scheduler.scheduleOnce(job);
+
+		Expect(this.scheduleOnceCalls.length).toBe(1);
+		Expect(this.scheduleOnceCalls[0].job.id).toBe('job-1_test-app');
+	}
+
+	@AsyncTest()
+	public async scheduleRecurringAppendsAppIdWhenMissing(): Promise<void> {
+		const scheduler = new SchedulerModify(this.mockSchedulerBridge, 'test-app');
+		const job: IRecurringSchedule = {
+			id: 'recurring-1',
+			interval: '5 minutes',
+			skipImmediate: true,
+			data: { roomId: 'abc' },
+		};
+
+		await scheduler.scheduleRecurring(job);
+
+		Expect(this.scheduleRecurringCalls.length).toBe(1);
+		Expect(this.scheduleRecurringCalls[0].appId).toBe('test-app');
+		Expect(this.scheduleRecurringCalls[0].job).toEqual({
+			...job,
+			id: 'recurring-1_test-app',
+		});
+		Expect(job.id).toBe('recurring-1');
+	}
+
+	@AsyncTest()
+	public async cancelJobAppendsAppIdWhenMissing(): Promise<void> {
+		const scheduler = new SchedulerModify(this.mockSchedulerBridge, 'test-app');
+
+		await scheduler.cancelJob('cleanup-job');
+
+		Expect(this.cancelJobCalls.length).toBe(1);
+		Expect(this.cancelJobCalls[0]).toEqual({
+			jobId: 'cleanup-job_test-app',
+			appId: 'test-app',
+		});
+	}
+
+	@AsyncTest()
+	public async cancelJobDoesNotAppendAppIdTwice(): Promise<void> {
+		const scheduler = new SchedulerModify(this.mockSchedulerBridge, 'test-app');
+
+		await scheduler.cancelJob('cleanup-job_test-app');
+
+		Expect(this.cancelJobCalls.length).toBe(1);
+		Expect(this.cancelJobCalls[0]).toEqual({
+			jobId: 'cleanup-job_test-app',
+			appId: 'test-app',
+		});
+	}
+
+	@AsyncTest()
+	public async cancelAllJobsUsesOnlyAppId(): Promise<void> {
+		const scheduler = new SchedulerModify(this.mockSchedulerBridge, 'test-app');
+
+		await scheduler.cancelAllJobs();
+
+		Expect(this.cancelAllJobsCalls.length).toBe(1);
+		Expect(this.cancelAllJobsCalls[0]).toBe('test-app');
+	}
+}
diff --git a/packages/message-parser/package.json b/packages/message-parser/package.json
index 4d8c3ab673e16..9a9e7bcc563cf 100644
--- a/packages/message-parser/package.json
+++ b/packages/message-parser/package.json
@@ -52,6 +52,7 @@
 		"@types/jest": "~30.0.0",
 		"@types/node": "~22.16.5",
 		"eslint": "~9.39.3",
+		"fast-check": "^4.6.0",
 		"jest": "~30.2.0",
 		"npm-run-all": "^4.1.5",
 		"peggy": "4.1.1",
diff --git a/packages/message-parser/src/grammar.pegjs b/packages/message-parser/src/grammar.pegjs
index 57084728715d5..2b24ec405ccb3 100644
--- a/packages/message-parser/src/grammar.pegjs
+++ b/packages/message-parser/src/grammar.pegjs
@@ -263,7 +263,16 @@ InlineEmoji = & { return !skipInlineEmoji; } emo:Emoji { return emo; }
 
 InlineEmoticon = & { return !skipInlineEmoji; } emo:Emoticon & (EmoticonNeighbor / InlineItemPattern) { skipInlineEmoji = false; return emo; }
 
+EscapedTimestampRules
+  = "\\" "<t:" rawDate:$(Unixtime / ISO8601Date / ISO8601DateWithoutMilliseconds / Timestamp) ":" format:TimestampType ">" {
+      return plain(`<t:${rawDate}:${format}>`);
+    }
+  / "\\" "<t:" rawDate:$(Unixtime / ISO8601Date / ISO8601DateWithoutMilliseconds / Timestamp) ">" {
+      return plain(`<t:${rawDate}>`);
+    }
+
 InlineItemPattern = Whitespace
+  / EscapedTimestampRules
   / TimestampRules
   / MaybeReferences
   / AutolinkedPhone
@@ -568,7 +577,7 @@ BoldEmoticon = & { return !skipBoldEmoji; } emo:Emoticon & (EmoticonNeighbor / B
 /* Strike */
 Strikethrough = [\x7E] [\x7E] @StrikethroughContent [\x7E] [\x7E] / [\x7E] @StrikethroughContent [\x7E]
 
-StrikethroughContent = text:(TimestampRules / Whitespace / InlineCode / MaybeReferences / UserMention / ChannelMention / MaybeItalic / MaybeBold / Emoji / Emoticon / AnyStrike / Line)+ {
+StrikethroughContent = text:(EscapedTimestampRules / TimestampRules / Whitespace / InlineCode / MaybeReferences / UserMention / ChannelMention / MaybeItalic / MaybeBold / Emoji / Emoticon / AnyStrike / Line)+ {
       return strike(reducePlainTexts(text));
     }
 
diff --git a/packages/message-parser/tests/escaped.test.ts b/packages/message-parser/tests/escaped.test.ts
index 78a759f7b2c6c..5266d1e86025c 100644
--- a/packages/message-parser/tests/escaped.test.ts
+++ b/packages/message-parser/tests/escaped.test.ts
@@ -15,6 +15,7 @@ test.each([
 	['\\# not a heading', [paragraph([plain('# not a heading')])]],
 	['\\[foo]: /url "not a reference"', [paragraph([plain('\\[foo]: /url "not a reference"')])]],
 	['\\&ouml; not a character entity', [paragraph([plain('\\&ouml; not a character entity')])]],
+	['\\<t:1708551317:R>', [paragraph([plain('<t:1708551317:R>')])]],
 ])('parses %p', (input, output) => {
 	expect(parse(input)).toMatchObject(output);
 });
diff --git a/packages/message-parser/tests/fuzz.test.ts b/packages/message-parser/tests/fuzz.test.ts
new file mode 100644
index 0000000000000..a3bf00a3158c3
--- /dev/null
+++ b/packages/message-parser/tests/fuzz.test.ts
@@ -0,0 +1,60 @@
+import fc from 'fast-check';
+
+import { parse } from '../src';
+
+const plainTextArbitrary = fc
+	.stringMatching(/[a-zA-Z0-9 ]{1,20}/)
+	.filter((value) => value.length > 0);
+
+const timestampArbitrary = fc
+	.integer({ min: 1_000_000_000, max: 2_000_000_000 })
+	.map((value) => `<t:${value}>`);
+
+const relativeTimestampArbitrary = fc
+	.integer({ min: 1_000_000_000, max: 2_000_000_000 })
+	.map((value) => `<t:${value}:R>`);
+
+const mentionArbitrary = fc
+	.stringMatching(/[a-z0-9._-]{1,12}/)
+	.map((value) => `@${value}`);
+
+const boldArbitrary = plainTextArbitrary.map((value) => `*${value}*`);
+
+const strikeArbitrary = fc.oneof(timestampArbitrary, relativeTimestampArbitrary, plainTextArbitrary).map((value) => `~${value}~`);
+
+const inlineCodeArbitrary = plainTextArbitrary.map((value) => `\`${value}\``);
+
+const parserInputArbitrary = fc
+	.array(
+		fc.oneof(
+			plainTextArbitrary,
+			timestampArbitrary,
+			relativeTimestampArbitrary,
+			mentionArbitrary,
+			boldArbitrary,
+			strikeArbitrary,
+			inlineCodeArbitrary,
+		),
+		{ minLength: 1, maxLength: 8 },
+	)
+	.map((parts) => parts.join(' '));
+
+describe('parser fuzz tests', () => {
+	test('parses valid parser-like inputs without throwing', () => {
+		fc.assert(
+			fc.property(parserInputArbitrary, (input) => {
+				expect(() => parse(input)).not.toThrow();
+			}),
+			{ numRuns: 300 },
+		);
+	});
+
+	test('is deterministic for valid parser-like inputs', () => {
+		fc.assert(
+			fc.property(parserInputArbitrary, (input) => {
+				expect(parse(input)).toEqual(parse(input));
+			}),
+			{ numRuns: 300 },
+		);
+	});
+});
\ No newline at end of file
diff --git a/packages/message-parser/tests/timestamp.test.ts b/packages/message-parser/tests/timestamp.test.ts
index 6652c280ee466..3cd95cef73d38 100644
--- a/packages/message-parser/tests/timestamp.test.ts
+++ b/packages/message-parser/tests/timestamp.test.ts
@@ -34,6 +34,7 @@ test.each([
 
 test.each([
 	['~<t:1708551317>~', [paragraph([strike([timestampNode('1708551317')])])]],
+	['~<t:1708551317:R>~', [paragraph([strike([timestampNode('1708551317', 'R')])])]],
 	['*<t:1708551317>*', [paragraph([bold([plain('<t:1708551317>')])])]],
 ])('parses %p', (input, output) => {
 	expect(parse(input)).toMatchObject(output);
diff --git a/yarn.lock b/yarn.lock
index f49420cef9f99..f3602e6cce97f 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -9713,6 +9713,7 @@ __metadata:
     "@types/jest": "npm:~30.0.0"
     "@types/node": "npm:~22.16.5"
     eslint: "npm:~9.39.3"
+    fast-check: "npm:^4.6.0"
     jest: "npm:~30.2.0"
     npm-run-all: "npm:^4.1.5"
     peggy: "npm:4.1.1"
@@ -22511,6 +22512,15 @@ __metadata:
   languageName: node
   linkType: hard
 
+"fast-check@npm:^4.6.0":
+  version: 4.6.0
+  resolution: "fast-check@npm:4.6.0"
+  dependencies:
+    pure-rand: "npm:^8.0.0"
+  checksum: 10/b53b88ebf6247ea0eaa7f3f6d8923035e0cfd6f78bc8c393754cc1ccbdb591756dfbff02058a136b472e011279594fa72c05a30378177d6055a08ad7ed1b823e
+  languageName: node
+  linkType: hard
+
 "fast-deep-equal@npm:^3.1.1, fast-deep-equal@npm:^3.1.3":
   version: 3.1.3
   resolution: "fast-deep-equal@npm:3.1.3"
@@ -32090,6 +32100,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"pure-rand@npm:^8.0.0":
+  version: 8.0.0
+  resolution: "pure-rand@npm:8.0.0"
+  checksum: 10/a5c84320f7337a6984e45cba969c804797535bb03b850897f0ee367d2d531feb489df220d475acc1dcf925c0832ed19a11c2928a94e9197ece5ad003368cb9c7
+  languageName: node
+  linkType: hard
+
 "pvtsutils@npm:^1.3.6":
   version: 1.3.6
   resolution: "pvtsutils@npm:1.3.6"