tests: cover visible output sanitization

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

Author: ricatix

tests/output-sanitization.test.ts

@@ -0,0 +1,143 @@
+import assert from "node:assert/strict"
+import test from "node:test"
+import type { PluginConfig } from "../lib/config"
+import { createTextCompleteHandler, createToolExecuteAfterHandler } from "../lib/hooks"
+import { injectMessageIds } from "../lib/messages/inject/inject"
+import { sanitizeVisibleOutput } from "../lib/messages/utils"
+import { createSessionState, type WithParts } from "../lib/state"
+
+function buildConfig(): PluginConfig {
+    return {
+        enabled: true,
+        debug: false,
+        pruneNotification: "off",
+        pruneNotificationType: "chat",
+        commands: {
+            enabled: true,
+            protectedTools: [],
+        },
+        manualMode: {
+            enabled: false,
+            automaticStrategies: true,
+        },
+        turnProtection: {
+            enabled: false,
+            turns: 4,
+        },
+        experimental: {
+            allowSubAgents: true,
+            customPrompts: false,
+        },
+        protectedFilePatterns: [],
+        compress: {
+            permission: "allow",
+            showCompression: false,
+            maxContextLimit: 150000,
+            minContextLimit: 50000,
+            nudgeFrequency: 5,
+            iterationNudgeThreshold: 15,
+            nudgeForce: "soft",
+            flatSchema: false,
+            protectedTools: [],
+            protectUserMessages: false,
+        },
+        strategies: {
+            deduplication: {
+                enabled: true,
+                protectedTools: [],
+            },
+            supersedeWrites: {
+                enabled: true,
+            },
+            purgeErrors: {
+                enabled: true,
+                turns: 4,
+                protectedTools: [],
+            },
+        },
+    }
+}
+
+test("sanitizeVisibleOutput strips DCP metadata and trailing blank lines", () => {
+    const result = sanitizeVisibleOutput(`bun install
+<dcp-message-id>m0045</dcp-message-id>
+
+
+<dcp-system-reminder>hidden</dcp-system-reminder>
+`)
+
+    assert.equal(result, "bun install")
+})
+
+test("tool.execute.after strips DCP metadata from visible tool output", async () => {
+    const handler = createToolExecuteAfterHandler()
+    const output = {
+        title: `bash
+<dcp-message-id>m0045</dcp-message-id>`,
+        output: `bun install v1.3.10
+<dcp-message-id>m0045</dcp-message-id>`,
+        metadata: {},
+    }
+
+    await handler({ tool: "bash", sessionID: "ses_1", callID: "call_1" }, output)
+
+    assert.equal(output.title, "bash")
+    assert.equal(output.output, "bun install v1.3.10")
+})
+
+test("experimental.text.complete strips DCP metadata from visible assistant text", async () => {
+    const handler = createTextCompleteHandler()
+    const output = {
+        text: `done
+<dcp-message-id>m0045</dcp-message-id>
+<dcp-system-reminder>hidden</dcp-system-reminder>`,
+    }
+
+    await handler({ sessionID: "ses_1", messageID: "msg_1", partID: "part_1" }, output)
+
+    assert.equal(output.text, "done")
+})
+
+test("injectMessageIds keeps assistant tool output clean and inserts a synthetic text part", () => {
+    const state = createSessionState()
+    state.messageIds.byRawId.set("assistant-1", "m0045")
+
+    const messages: WithParts[] = [
+        {
+            info: {
+                id: "assistant-1",
+                role: "assistant",
+                sessionID: "ses_1",
+                agent: "assistant",
+                time: { created: 1 },
+            } as WithParts["info"],
+            parts: [
+                {
+                    id: "tool-part-1",
+                    sessionID: "ses_1",
+                    messageID: "assistant-1",
+                    type: "tool",
+                    callID: "call_1",
+                    tool: "bash",
+                    state: {
+                        status: "completed",
+                        input: {},
+                        title: "bash",
+                        output: "bun install v1.3.10",
+                        metadata: {},
+                        time: { start: 1, end: 2 },
+                    },
+                },
+            ],
+        },
+    ]
+
+    injectMessageIds(state, buildConfig(), messages)
+
+    assert.equal(messages[0].parts[0].type, "text")
+    assert.equal(messages[0].parts[0].synthetic, true)
+    assert.match(messages[0].parts[0].text, /<dcp-message-id>m0045<\/dcp-message-id>/)
+    assert.equal(messages[0].parts[1].type, "tool")
+    assert.equal(messages[0].parts[1].state.status, "completed")
+    assert.equal(messages[0].parts[1].state.output, "bun install v1.3.10")
+})