update docs

docs/troubleshooting.md

@@ -5,6 +5,9 @@ Read the complete command error and its log before retrying. Build logs are in
 On FDS, `fds bay N`, `fds profiles` and `fds power status` report the relevant
 operation state. Append `--help` to a command for accepted options.
 
+For physical Pi startup, use [first-boot troubleshooting](hardware-setup.md#when-the-first-boot-fails).
+For the Paperlike on HDMI plus USB, use [Dasung diagnostics](dasung.md#diagnose-a-connection-problem).
+
 | Symptom | Resolution |
 | --- | --- |
 | Build disk is full | Stop builds and VMs; run `make clean-preview`, then `make clean`. See [retention rules](cleanup.md). |
@@ -12,7 +15,7 @@ operation state. Append `--help` to a command for accepted options.
 | Bubblewrap/user namespace failure | Check that the host permits unprivileged namespaces. Run the check in [setup](getting-started.md); do not switch software builds to root. |
 | Void checkout is unprepared | Bootstrap the checkout using upstream xbps-src instructions, then select it with `--void-packages`. |
 | Stale generated overlay/source package | Compare the source and generated copy. Preserve independent edits, remove only that generated copy, and retry. Never overwrite tracked upstream templates. |
-| Output already exists | Use a new output directory, cartridge image, preview or emulator session. Creation does not overwrite existing outputs. |
+| Output already exists | Use a new output directory, cartridge image or preview. A stopped emulator session can be restarted; see below. |
 | Executable architecture or tree integrity error | Rebuild the source package and cartridge. FDS cannot run an invalid payload. |
 | A command is unavailable | Wait for `MOUNTED READ ONLY`, inspect `fds --json bay N`, and use its qualified command alias. Run `hash -r` after removal if Bash retained an old path. |
 | Empty or unconfigured physical bays | Run `fds topology` and calibrate the machine's bay map. Do not infer slots from disk names. |