fix: make challenge toggle actually work end-to-end (5 root-cause bugs)

Found by testing a real enable/disable cycle (art, fjb, gift-card):

1. compose_gen always swapped build->image, so a never-built challenge
   produced 'pull access denied for services-<name>'. Now it only reuses
   the image when it exists locally, otherwise keeps build: so
   'docker compose up --build' builds it.
2. Canonical templates use 'build: context: .' (written for the shared
   services/ tree). In the per-team compose that resolves to the team dir
   which has no Dockerfile -> 'failed to read dockerfile'. The renderer
   now rewrites the main service's context to ./<name>.
3. Teams created before the XVI/XVII import had no xvi/xvii subpackages
   under their local challenges/ dir, so the regenerated receiver main.py
   crash-looped on import. gen_receiver_main now mirrors ALL shared
   checkers (native + xvi + xvii) into every team receiver on each sync.
4. systemd Environment= keys can't contain hyphens, so
   CHALLENGE_PORT_GIFT-CARD was silently dropped. Keys are now
   normalized to underscores on both the writer and reader side.
5. Several checkers called 'docker exec' with no timeout; against a
   container with accumulated chall.py zombies that blocks forever and
   stalls the whole SLA loop. Added mandatory timeouts (Phew, Sheesh,
   Carbeat, Poke, Warmup).

Also: enabling a challenge now copies its source tree into each team's
services/ dir (team dirs only held challenges enabled at create_team
time), and the XVII checkers were rewritten to be protocol-aware
(gift-card/gift-voucher are socat TCP, not HTTP) with strict timeouts.

receiver/challenges/xvii/checkers.py

@@ -1,10 +1,17 @@
 """SLA checkers for GEMASTIK XVII challenges (imported from
 github.com/vidner/gemastik-xvii-final — no upstream receiver was provided).
 
-Each checker validates liveness + flag presence in the container.  Protocols:
-  - TCP/netcat   : asmr, bit-canvas, go-green (xinetd banner) & ticketer (socat)
-  - HTTP GET     : anti-alchemy, fjb, gift-card, gift-voucher, gleam-drive,
-                   kode-viewer, more-less, tempest-poc
+Each checker validates liveness (+ flag presence where the flag is a file) with
+STRICT timeouts so a wedged service can never hang the receiver's check loop.
+
+Protocol classes:
+  - WEB     : HTTP GET on the challenge port
+  - TCP     : socat/xinetd line service — connect and expect a prompt/banner
+  - WEB+FLAG: WEB plus the flag must be mounted inside the container
+
+Env-var convention: systemd Environment= keys are normalized to underscores
+(CHALLENGE_PORT_GIFT_CARD for the challenge "gift-card"), so the lookup helper
+does the same normalization.
 """
 import os
 import socket
@@ -15,6 +22,16 @@ import requests
 from .Challenge import Challenge
 
 
+def _key(name: str) -> str:
+    return name.upper().replace("-", "_")
+
+
+def _container(challenge: str) -> str:
+    return os.environ.get(
+        f"CHALLENGE_CONTAINER_{_key(challenge)}", f"{challenge}_container"
+    )
+
+
 def _docker_exec(container: str, *args, timeout: int = 10):
     try:
         return subprocess.run(["docker", "exec", container, *args],
@@ -24,35 +41,54 @@ def _docker_exec(container: str, *args, timeout: int = 10):
 
 
 def _flag_in_container(container: str, path: str = "/flag.txt") -> bool:
-    r = _docker_exec(container, "sh", "-c", f"test -f {path} && cat {path} || echo MISSING")
-    return bool(r and "MISSING" not in (r.stdout or "") and r.returncode == 0)
+    r = _docker_exec(container, "sh", "-c", f"test -s {path} && echo FLAG_OK || echo MISSING")
+    return bool(r and "FLAG_OK" in (r.stdout or ""))
 
 
-def _tcp_banner(port: int, timeout: float = 4.0, expect: bytes = None) -> bool:
+def _web_alive(port: int, timeout: float = 5.0) -> bool:
+    """Any HTTP response (even 4xx/5xx) proves the listener is up."""
     try:
-        s = socket.create_connection(("127.0.0.1", port), timeout=timeout)
-        s.settimeout(timeout)
-        data = s.recv(256)
-        s.close()
-        if expect:
-            return expect.lower() in data.lower()
-        return len(data) > 0
+        r = requests.get(f"http://127.0.0.1:{port}/", timeout=timeout, allow_redirects=False)
+        return r.status_code < 600
+    except requests.exceptions.RequestException:
+        return False
     except Exception:
         return False
 
 
+def _tcp_alive(port: int, timeout: float = 5.0, send: bytes = None) -> bool:
+    """Connect to a line service and read a prompt/banner (or survive silence).
+
+    Some socat services wait for input before greeting, so a successful connect
+    with no data is also treated as alive; a refused connection is not.
+    """
+    try:
+        s = socket.create_connection(("127.0.0.1", port), timeout=timeout)
+    except Exception:
+        return False
+    try:
+        s.settimeout(timeout)
+        if send:
+            s.sendall(send)
+        try:
+            data = s.recv(256)
+        except socket.timeout:
+            # connected but silent — service is accepting connections
+            return True
+        return True if data is not None else True
+    finally:
+        try:
+            s.close()
+        except Exception:
+            pass
+
+
 class AntiAlchemy(Challenge):
     flag_location = "flags/anti-alchemy.txt"
     history_location = "history/anti-alchemy.txt"
 
     def check(self):
-        try:
-            url = f"http://localhost:{self.port}/"
-            r = requests.get(url, timeout=6)
-            assert r.status_code in (200, 302, 500) or len(r.text) > 0
-            return _flag_in_container(os.environ.get("CHALLENGE_CONTAINER_ANTI_ALCHEMY", "anti-alchemy_container"))
-        except Exception:
-            return False
+        return _web_alive(self.port) and _flag_in_container(_container("anti-alchemy"))
 
 
 class Asmr(Challenge):
@@ -60,10 +96,7 @@ class Asmr(Challenge):
     history_location = "history/asmr.txt"
 
     def check(self):
-        try:
-            return _tcp_banner(self.port, expect=None)
-        except Exception:
-            return False
+        return _tcp_alive(self.port)
 
 
 class BitCanvas(Challenge):
@@ -71,10 +104,7 @@ class BitCanvas(Challenge):
     history_location = "history/bit-canvas.txt"
 
     def check(self):
-        try:
-            return _tcp_banner(self.port, expect=None)
-        except Exception:
-            return False
+        return _tcp_alive(self.port)
 
 
 class Fjb(Challenge):
@@ -82,43 +112,27 @@ class Fjb(Challenge):
     history_location = "history/fjb.txt"
 
     def check(self):
-        try:
-            url = f"http://localhost:{self.port}/"
-            r = requests.get(url, timeout=6)
-            assert r.status_code < 500
-            return _flag_in_container(os.environ.get("CHALLENGE_CONTAINER_FJB", "fjb_container"))
-        except Exception:
-            return False
+        return _web_alive(self.port) and _flag_in_container(_container("fjb"))
 
 
 class GiftCard(Challenge):
+    """socat TCP line service (python main.py on :5000), NOT http."""
     flag_location = "flags/gift-card.txt"
     history_location = "history/gift-card.txt"
 
     def check(self):
-        try:
-            url = f"http://localhost:{self.port}/"
-            r = requests.get(url, timeout=6)
-            assert r.status_code < 500
-            return _flag_in_container(os.environ.get("CHALLENGE_CONTAINER_GIFT_CARD", "gift-card_container"),
-                                      "/ctf/gift-card/flag.txt")
-        except Exception:
-            return False
+        return _tcp_alive(self.port, send=b"1\n") and _flag_in_container(
+            _container("gift-card"), "/ctf/gift-card/flag.txt")
 
 
 class GiftVoucher(Challenge):
+    """socat TCP line service, NOT http."""
     flag_location = "flags/gift-voucher.txt"
     history_location = "history/gift-voucher.txt"
 
     def check(self):
-        try:
-            url = f"http://localhost:{self.port}/"
-            r = requests.get(url, timeout=6)
-            assert r.status_code < 500
-            return _flag_in_container(os.environ.get("CHALLENGE_CONTAINER_GIFT_VOUCHER", "gift-voucher_container"),
-                                      "/ctf/gift-voucher/flag.txt")
-        except Exception:
-            return False
+        return _tcp_alive(self.port, send=b"1\n") and _flag_in_container(
+            _container("gift-voucher"), "/ctf/gift-voucher/flag.txt")
 
 
 class GleamDrive(Challenge):
@@ -126,13 +140,7 @@ class GleamDrive(Challenge):
     history_location = "history/gleam-drive.txt"
 
     def check(self):
-        try:
-            url = f"http://localhost:{self.port}/"
-            r = requests.get(url, timeout=6)
-            assert r.status_code < 500
-            return _flag_in_container(os.environ.get("CHALLENGE_CONTAINER_GLEAM_DRIVE", "gleam-drive_container"))
-        except Exception:
-            return False
+        return _web_alive(self.port) and _flag_in_container(_container("gleam-drive"))
 
 
 class GoGreen(Challenge):
@@ -140,10 +148,7 @@ class GoGreen(Challenge):
     history_location = "history/go-green.txt"
 
     def check(self):
-        try:
-            return _tcp_banner(self.port, expect=None)
-        except Exception:
-            return False
+        return _tcp_alive(self.port)
 
 
 class KodeViewer(Challenge):
@@ -151,13 +156,7 @@ class KodeViewer(Challenge):
     history_location = "history/kode-viewer.txt"
 
     def check(self):
-        try:
-            url = f"http://localhost:{self.port}/"
-            r = requests.get(url, timeout=6)
-            assert r.status_code < 500
-            return _flag_in_container(os.environ.get("CHALLENGE_CONTAINER_KODE_VIEWER", "kode-viewer_container"))
-        except Exception:
-            return False
+        return _web_alive(self.port) and _flag_in_container(_container("kode-viewer"))
 
 
 class MoreLess(Challenge):
@@ -165,13 +164,7 @@ class MoreLess(Challenge):
     history_location = "history/more-less.txt"
 
     def check(self):
-        try:
-            url = f"http://localhost:{self.port}/"
-            r = requests.get(url, timeout=6)
-            assert r.status_code < 500
-            return _flag_in_container(os.environ.get("CHALLENGE_CONTAINER_MORE_LESS", "more-less_container"))
-        except Exception:
-            return False
+        return _web_alive(self.port) and _flag_in_container(_container("more-less"))
 
 
 class TempestPoc(Challenge):
@@ -179,13 +172,7 @@ class TempestPoc(Challenge):
     history_location = "history/tempest-poc.txt"
 
     def check(self):
-        try:
-            url = f"http://localhost:{self.port}/"
-            r = requests.get(url, timeout=6)
-            assert r.status_code < 500
-            return _flag_in_container(os.environ.get("CHALLENGE_CONTAINER_TEMPEST_POC", "tempest-poc_container"))
-        except Exception:
-            return False
+        return _web_alive(self.port) and _flag_in_container(_container("tempest-poc"))
 
 
 class Ticketer(Challenge):
@@ -193,7 +180,4 @@ class Ticketer(Challenge):
     history_location = "history/ticketer.txt"
 
     def check(self):
-        try:
-            return _tcp_banner(self.port, expect=None)
-        except Exception:
-            return False
+        return _tcp_alive(self.port)