fix(openclaw): surface .openclaw-system.md fallback when agents add fails

Addresses codex review P2 on install.sh:103-111.

When `openclaw` is on PATH but `agents add --workspace` fails (older forks
that don't support the subcommand or flag), the previous failure message
told the user to retry the same unsupported command. That left users on
older OpenClaw builds without a working setup even though install.sh had
already written `.openclaw-system.md` — the exact backward-compat include
those builds can use.

Now when registration fails (not "already exists"), the installer points
at `.openclaw-system.md` with `openclaw --system-prompt-file <abs>` as
the fallback, and keeps the retry command as a secondary option. Same
change on the "CLI not on PATH" branch, since we can't know what fork
the user is about to install.

Mirrored in install.ps1 (success, failure, catch, and not-on-PATH branches).

Author: codejunkie99

install.ps1

@@ -117,18 +117,24 @@ switch ($Adapter) {
                 } elseif ($ocOutJoined -match '(?i)already exists') {
                     Write-Host "  ✓ already registered (idempotent re-run). run: openclaw --agent $ocAgentName"
                 } else {
-                    Write-Host "  ! 'openclaw agents add' failed (details above). retry manually:"
-                    Write-Host "      openclaw agents add `"$ocAgentName`" --workspace `"$ocAbs`""
+                    Write-Host "  ! 'openclaw agents add' failed (details above)."
+                    Write-Host "    if your OpenClaw fork does not support 'agents add --workspace',"
+                    Write-Host "    fall back to the system-prompt include we wrote:"
+                    Write-Host "      openclaw --system-prompt-file `"$ocAbs\.openclaw-system.md`""
+                    Write-Host "    otherwise retry: openclaw agents add `"$ocAgentName`" --workspace `"$ocAbs`""
                 }
             } catch {
                 Write-Host "  ! 'openclaw agents add' errored: $_"
-                Write-Host "    retry manually:"
-                Write-Host "      openclaw agents add `"$ocAgentName`" --workspace `"$ocAbs`""
+                Write-Host "    fall back to the system-prompt include:"
+                Write-Host "      openclaw --system-prompt-file `"$ocAbs\.openclaw-system.md`""
+                Write-Host "    or retry: openclaw agents add `"$ocAgentName`" --workspace `"$ocAbs`""
             }
         } else {
-            Write-Host "  ! 'openclaw' CLI not found on PATH. after installing OpenClaw, run:"
+            Write-Host "  ! 'openclaw' CLI not found on PATH. after installing OpenClaw, try:"
             Write-Host "      openclaw agents add `"$ocAgentName`" --workspace `"$ocAbs`""
-            Write-Host "    then: openclaw --agent $ocAgentName"
+            Write-Host "      openclaw --agent $ocAgentName"
+            Write-Host "    or, on forks without 'agents add', use the system-prompt include:"
+            Write-Host "      openclaw --system-prompt-file `"$ocAbs\.openclaw-system.md`""
         }
     }
     'hermes' {

install.sh

@@ -107,13 +107,18 @@ case "$ADAPTER" in
       elif printf '%s' "$OC_OUT" | grep -qi "already exists"; then
         echo "  ✓ already registered (idempotent re-run). run: openclaw --agent $OC_AGENT_NAME"
       else
-        echo "  ! 'openclaw agents add' failed (details above). retry manually:"
-        echo "      openclaw agents add \"$OC_AGENT_NAME\" --workspace \"$OC_ABS\""
+        echo "  ! 'openclaw agents add' failed (details above)."
+        echo "    if your OpenClaw fork does not support 'agents add --workspace',"
+        echo "    fall back to the system-prompt include we wrote:"
+        echo "      openclaw --system-prompt-file \"$OC_ABS/.openclaw-system.md\""
+        echo "    otherwise retry: openclaw agents add \"$OC_AGENT_NAME\" --workspace \"$OC_ABS\""
       fi
     else
-      echo "  ! 'openclaw' CLI not found on PATH. after installing OpenClaw, run:"
+      echo "  ! 'openclaw' CLI not found on PATH. after installing OpenClaw, try:"
       echo "      openclaw agents add \"$OC_AGENT_NAME\" --workspace \"$OC_ABS\""
-      echo "    then: openclaw --agent $OC_AGENT_NAME"
+      echo "      openclaw --agent $OC_AGENT_NAME"
+      echo "    or, on forks without 'agents add', use the system-prompt include:"
+      echo "      openclaw --system-prompt-file \"$OC_ABS/.openclaw-system.md\""
     fi
     ;;
   hermes)