[Bug] Touch/pen input disabled when native_pen_touch omitted from config (v2026.808 regression)

[AliceJump]

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Describe the Bug

After updating Sunshine from the old version to the new version, I found
that multi-touch input is always unusable. The client (Moonlight Android,
https://github.com/Axixi2233/moonlight-android) was unchanged — it only broke
after the Sunshine update. I noticed the old Sunshine version had this feature
working, so I ran an experiment:

• Old version (touch works): 2025.924.154138
• New version (touch broken): 2026.808.164219

1. Used the Web UI to change the option to unchecked (disable) and saved.
   After saving, the config contained native_pen_touch = disabled. Restarted,
   touch was unusable.
2. Re-enabled it via the Web UI. After saving, the key disappeared from the
   config file. Restarted, touch was still unusable.
3. Directly edited the config file to force native_pen_touch = enabled.
   Touch became usable.

Corresponding logs: see scenarios 1/2/3 in "Additional Context".

Expected Behavior

Multi-touch input should work after updating to the new version, matching the
behavior of the old version. The native_pen_touch option should be enabled by
default so touch input works even when the key is absent from the config.

Additional Context

• Sunshine version: 2026.808.164219 (commit 25c06d79), Windows 11
• Client: Moonlight Android (fork) - https://github.com/Axixi2233/moonlight-android
• Full (redacted) logs for all three scenarios: https://gist.github.com/AliceJump/e4e893dba40b455bb0012cb84efe7932

Scenario 1 - Web UI disable + save (config: 'native_pen_touch' = disabled) — touch unusable:

Startup:

[2026-08-18 08:07:17.574]: Info: Sunshine version: 2026.808.164219 commit: 25c06d79b54f3d092d3fedd5f5ba44989f394692
[2026-08-18 08:07:17.574]: Info: Package Publisher: LizardByte
[2026-08-18 08:07:17.574]: Info: Publisher Website: https://app.lizardbyte.dev
[2026-08-18 08:07:17.574]: Info: Get support: https://app.lizardbyte.dev/support
[2026-08-18 08:07:17.574]: Info: config: 'native_pen_touch' = disabled
[2026-08-18 08:07:17.574]: Info: Provided workaround settings for SettingsManager:

Session:

[2026-08-18 08:07:23.592]: Info: Found H.264 encoder: h264_nvenc [nvenc]
[2026-08-18 08:07:23.592]: Info: Found HEVC encoder: hevc_nvenc [nvenc]
[2026-08-18 08:07:23.592]: Info: Executing [Desktop]
[2026-08-18 08:07:23.672]: Info: New streaming session started [active sessions: 1]
[2026-08-18 08:07:23.858]: Info: nvprefs: No need to modify application profile settings
[2026-08-18 08:07:23.925]: Info: CLIENT CONNECTED
[2026-08-18 08:07:24.198]: Info: Opus initialized: 48 kHz, 2 channels, 512 kbps (total), LOWDELAY
[2026-08-18 08:07:24.255]: Info: Using realtime GPU priority

Stop:

[2026-08-18 08:09:32.696]: Info: Interrupt handler called
[2026-08-18 08:09:32.706]: Info: Starting async encoder teardown
[2026-08-18 08:09:33.055]: Info: Unregistered Sunshine mDNS service

Note: no Creating virtual touch input device line appears during the whole session.

Scenario 2 - Web UI enable + save (key omitted from config, no load line) — touch unusable:

Startup:

[2026-08-18 08:09:36.101]: Info: Sunshine version: 2026.808.164219 commit: 25c06d79b54f3d092d3fedd5f5ba44989f394692
[2026-08-18 08:09:36.101]: Info: Package Publisher: LizardByte
[2026-08-18 08:09:36.101]: Info: Publisher Website: https://app.lizardbyte.dev
[2026-08-18 08:09:36.101]: Info: Get support: https://app.lizardbyte.dev/support

Note: there is no config: 'native_pen_touch' = ... line because the key is absent.
Session:

[2026-08-18 08:09:41.089]: Info: Found HEVC encoder: hevc_nvenc [nvenc]
[2026-08-18 08:09:41.089]: Info: Executing [Desktop]
[2026-08-18 08:09:41.181]: Info: New streaming session started [active sessions: 1]
[2026-08-18 08:09:41.367]: Info: nvprefs: No need to modify application profile settings
[2026-08-18 08:09:41.435]: Info: CLIENT CONNECTED
[2026-08-18 08:09:41.701]: Info: Opus initialized: 48 kHz, 2 channels, 512 kbps (total), LOWDELAY

Note: no Creating virtual touch input device line appears during the whole session.

Scenario 3 - manually set native_pen_touch = enabled + restart — touch works:

Startup:

[2026-08-18 08:11:11.907]: Info: Sunshine version: 2026.808.164219 commit: 25c06d79b54f3d092d3fedd5f5ba44989f394692
[2026-08-18 08:11:11.907]: Info: Package Publisher: LizardByte
[2026-08-18 08:11:11.907]: Info: Publisher Website: https://app.lizardbyte.dev
[2026-08-18 08:11:11.907]: Info: Get support: https://app.lizardbyte.dev/support
[2026-08-18 08:11:11.907]: Info: config: 'native_pen_touch' = enabled
[2026-08-18 08:11:11.908]: Info: Provided workaround settings for SettingsManager:

Session:

[2026-08-18 08:11:24.741]: Info: Found H.264 encoder: h264_nvenc [nvenc]
[2026-08-18 08:11:24.741]: Info: Found HEVC encoder: hevc_nvenc [nvenc]
[2026-08-18 08:11:24.741]: Info: Executing [Desktop]
[2026-08-18 08:11:24.816]: Info: New streaming session started [active sessions: 1]
[2026-08-18 08:11:25.007]: Info: nvprefs: No need to modify application profile settings
[2026-08-18 08:11:25.067]: Info: CLIENT CONNECTED
[2026-08-18 08:11:25.362]: Info: Opus initialized: 48 kHz, 2 channels, 512 kbps (total), LOWDELAY
[2026-08-18 08:11:25.397]: Info: Using realtime GPU priority
[2026-08-18 08:11:26.066]: Info: Creating virtual touch input device

Note: Creating virtual touch input device appears once the client sends touch input.