diff --git a/services/wolf.sh b/services/wolf.sh
index e9a4c3b..fcf2f9a 100644
--- a/services/wolf.sh
+++ b/services/wolf.sh
@@ -948,14 +948,15 @@ UDEV
     # ti99sim-sdl (billzajac/ti99sim) is the real target — genuine SDL2
     # joystick/gamepad support, confirmed against its own README — but it's
     # source-only with no AppImage, so unlike Azahar/PCSX2/Dolphin/Cemu this
-    # installer can't just download a working binary: building it here would
-    # mean compiling against the HOST's glibc/SDL2 while the binary actually
-    # needs to run inside the ES-DE container's own (different) runtime, and
-    # that mismatch isn't something to guess at blind. The custom system
+    # installer can't just download a working binary. Building it against the
+    # HOST's glibc/SDL2 risks a mismatch against the ES-DE container's own
+    # (different) runtime, so instead it's built INSIDE a throwaway container
+    # running the exact same image ES-DE itself runs
+    # (ghcr.io/games-on-whales/es-de:edge) — that's what actually guarantees
+    # compatibility rather than just avoiding the question. The custom system
     # definition below always gets written — cheap and correct regardless —
     # pointing at emulators/ti99sim-sdl (the same ~/Applications convention
-    # every other standalone emulator here uses), so dropping a working
-    # binary there is the only remaining step.
+    # every other standalone emulator here uses).
     echo ""
     local _GET_TI99=""
     prompt_yn "Set up TI-99/4A as its own ES-DE system (artwork scraping, gameplay-time tracking)? (y/n):" "n" _GET_TI99
@@ -984,18 +985,49 @@ XMLEOF
             log_info "TI-99/4A system definition already present — left as-is."
         fi
         echo ""
-        log_warning "ti99sim-sdl itself still needs to be built and placed by hand — this installer can't"
-        log_warning "safely cross-compile a binary that's guaranteed to run inside the ES-DE container:"
-        log_info "  1. git clone https://github.com/billzajac/ti99sim.git && cd ti99sim && make"
-        log_info "     (needs libsdl2-dev — same build machine/container the ES-DE image itself runs on"
-        log_info "     gives the best chance the result actually runs; a plain host build may hit a"
-        log_info "     glibc/SDL2 mismatch inside the container)"
-        log_info "  2. Copy the resulting ti99sim-sdl binary to:"
-        log_info "     $GAME_STORAGE_DIR/emulators/ti99sim-sdl"
-        log_info "  3. You'll also need your own TI-99/4A console ROM + GROM dump (real console"
-        log_info "     firmware, same legal situation as any other console BIOS) — ti99sim's own"
-        log_info "     README covers where it expects that once you have it."
-        log_info "  4. Drop .ctg/.rpk/.bin cartridge files into roms/ti994a/"
+        if [ ! -x "$GAME_STORAGE_DIR/emulators/ti99sim-sdl" ]; then
+            # Build inside a container running the EXACT SAME image ES-DE
+            # itself runs (ghcr.io/games-on-whales/es-de:edge), not the host —
+            # that's what actually eliminates the glibc/SDL2 mismatch risk,
+            # rather than just noting it and asking the user to build blind.
+            # --entrypoint overrides GoW's own init (which normally drops to
+            # the unprivileged 'retro' user), so -u root is explicit here for
+            # apt-get; the built binary only ever runs later as 'retro',
+            # unaffected by what user built it.
+            log_info "Building ti99sim-sdl inside the same container image ES-DE runs (matches its"
+            log_info "glibc/SDL2 exactly, so the result is guaranteed compatible)..."
+            # `make` alone leaves the binary under src/, not the repo root —
+            # confirmed against the project's own README ("all the
+            # executables are left in their corresponding directories").
+            # `make install` is the project's own reliable way to collect
+            # it (copies to /opt/ti99sim/bin, symlinks into
+            # /usr/local/bin), so use that instead of guessing the exact
+            # build subpath.
+            if docker run --rm -u root --entrypoint /bin/bash \
+                -v "$GAME_STORAGE_DIR/emulators:/output" \
+                ghcr.io/games-on-whales/es-de:edge -c '
+                    set -e
+                    apt-get update -qq
+                    apt-get install -y -qq git build-essential libsdl2-dev ca-certificates
+                    git clone -q https://github.com/billzajac/ti99sim.git /tmp/ti99sim
+                    cd /tmp/ti99sim
+                    make
+                    make install
+                    cp /usr/local/bin/ti99sim-sdl /output/ti99sim-sdl
+                '; then
+                chmod +x "$GAME_STORAGE_DIR/emulators/ti99sim-sdl"
+                chown "$ACTUAL_USER:$ACTUAL_USER" "$GAME_STORAGE_DIR/emulators/ti99sim-sdl"
+                log_success "ti99sim-sdl built and installed -> $GAME_STORAGE_DIR/emulators/ti99sim-sdl"
+            else
+                log_warning "Build failed — check the docker output above. Retry later with: sudo ./setup.sh wolf"
+            fi
+        else
+            log_info "ti99sim-sdl already present — skipping build."
+        fi
+        log_info "The one thing this can't do for you: your own TI-99/4A console ROM + GROM dump"
+        log_info "(real console firmware, same legal situation as any other BIOS) — ti99sim-sdl's"
+        log_info "own README covers exactly where it expects that once you have it."
+        log_info "Then just drop .ctg/.rpk/.bin cartridge files into roms/ti994a/"
     fi
 
     # ── App selection ─────────────────────────────────────────────────────────
@@ -3474,19 +3506,20 @@ tracking) via a custom system definition at
 service, which is browser-based and isn't something ES-DE can launch as a
 system.
 
-The emulator itself, \`ti99sim-sdl\` (real SDL2 gamepad support), isn't
-auto-downloaded — it has no AppImage, and building it on the host risks a
-glibc/SDL2 mismatch against the ES-DE container's own runtime that isn't
-safe to guess at blind. Build it yourself and drop the binary at
-\`emulators/ti99sim-sdl\`:
-\`\`\`bash
-git clone https://github.com/billzajac/ti99sim.git && cd ti99sim && make
-\`\`\`
-(needs \`libsdl2-dev\`). You'll also need your own TI-99/4A console ROM +
-GROM dump — same legal situation as any other console BIOS, and not
-something this installer supplies — ti99sim's own README covers where it
-expects that. Then drop \`.ctg\`/\`.rpk\`/\`.bin\` cartridge files into
-\`roms/ti994a/\`.
+The emulator itself, \`ti99sim-sdl\` (real SDL2 gamepad support), has no
+AppImage — so instead of a plain host build (which risks a glibc/SDL2
+mismatch against the ES-DE container's own runtime), this installer builds
+it inside a throwaway container running the exact same image ES-DE itself
+runs (\`ghcr.io/games-on-whales/es-de:edge\`), guaranteeing compatibility,
+and drops the result at \`emulators/ti99sim-sdl\` automatically. Re-run
+\`sudo ./setup.sh wolf\` if the build ever needs retrying (network hiccup,
+etc.) — it skips the build if the binary's already there.
+
+The one thing this can't do for you: your own TI-99/4A console ROM + GROM
+dump — same legal situation as any other console BIOS, and not something
+any installer can supply — ti99sim-sdl's own README covers exactly where
+it expects that once you have it. Then just drop \`.ctg\`/\`.rpk\`/\`.bin\`
+cartridge files into \`roms/ti994a/\`.
 
 ## MAME: sample packs showing up as games
 MAME sample packs (audio for a handful of older analog-sound games) use the