Fix terminal sticky scroll returning disposed commands after clearBuffer

[Copilot]

Description

Terminal sticky scroll fails on second task run when presentation.clear: true is configured. getCommandForLine() returns disposed commands because it compares marker line numbers without checking validity—disposed markers have line === -1, making -1 <= 0 evaluate true.

Changes

Modified getCommandForLine() in commandDetectionCapability.ts:

• Filter commands where marker.line === -1 (disposed after clearBuffer())
• Check first command marker validity before iteration
• Added inline comment explaining disposal state

Added test coverage:

• Verifies disposed commands are skipped after xterm.clear()
• Confirms current partial command is returned instead of stale command

Example

// Before: returned disposed command with marker.line === -1
const command = capability.getCommandForLine(0);

// After: skips disposed commands, returns current command
if (commandMarker.line !== -1 && commandMarker.line <= line) {
    return this.commands[i];
}

Related to #199305

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Task terminal sticky scroll bug after being cleared</issue_title>
<issue_description>
Type: Bug

With the following task.json (and a sufficiently small terminal), running the task twice makes the terminal sticky scroll feature bug, as the command is not printed twice after the task's terminal is cleared.

This is very similar to #199305

{
	"version": "2.0.0",
	"tasks": [
		{
			"label": "whatever",
			"type": "shell",
			"command": "echo 'manatee\nchocolate\ndistribute\npride\nfox\nfree\nmethod\ntradition\npenny\nfreight\nproductive\nconference'",
			"presentation": { "clear": true }
		}
	]
}

VS Code version: Code 1.106.2 (1e3c50d, 2025-11-19T16:56:50.023Z)
OS version: Linux x64 6.17.8-arch1-1
Modes:

Extensions (10)

Extension	Author (truncated)	Version
copilot-chat	Git	0.33.3
rainbow-csv	mec	3.23.0
debugpy	ms-	2025.16.0
python	ms-	2025.18.0
vscode-pylance	ms-	2025.10.2
vscode-python-envs	ms-	1.12.0
remote-ssh	ms-	0.120.0
remote-ssh-edit	ms-	0.87.0
hexeditor	ms-	1.11.1
remote-explorer	ms-	0.5.0

A/B Experiments

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e5gg6876:31282496
pythonrdcb7:31342333
aj953862:31281341
nes-set-on:31351930
6abeh943:31336334
envsdeactivate2:31353495
cloudbuttont:31379625
todos-1:31405332
qwen_all_req:31402696
treatment_gpt5applypatchexclusively:31412086
3efgi100_wstrepl:31403338
trigger-command-fix:31379601
auto_model_enabled:31385282
use-responses-api:31390855
6j29d282:31407606
ec5jj548:31422691
copilot-nes-oct-t:31418199
cmp-ext-treat:31426748
cp_cls_c_966_ss:31426491
defaultvisibility:31426295
expandedtokens:31426297
c0683394:31419495
ief76360:31426358
g0h3h215:31426582
b53de340:31426751
fa76a614:31426783
38bie571_auto:31426784

<agent_instructions>Investigate and tell me what happens when terminal is re-used for tasks.
What happens with output. Scrollback, viewport of that task termianl. When task are first run, secondly run. </agent_instructions>

Comments on the Issue (you are @copilot in this section)

@anthonykim1 Thanks for the issue! Will investigate. Need to figure out what happens when we re-run task in same terminal.

• Fixes Task terminal sticky scroll bug after being cleared #280025

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