fix(stage-1a): refuse to serve when MCP requirements cannot be read

entrypoint.sh discarded the exit status of the python overlay builder, so
an unparseable /etc/agency/mcp-requirements.json started the server with
MCP servers that should have been disabled, contradicting the stage-1a
overlay requirement. The entrypoint now exits 64 naming the file.

Evidence: docs/evidence/1a/entrypoint-mcp-requirements-failclosed.log (a
container started with a malformed requirements file exits 64, is not
running, and its log names the file). The image was rebuilt and checks
02/03/04 pass against it.

docs/evidence/1a/entrypoint-mcp-requirements-failclosed.log

@@ -0,0 +1,16 @@
+Entrypoint fail-closed on an unparseable /etc/agency/mcp-requirements.json.
+Sabotage/premise: the mounted requirements file is invalid JSON; before this
+fix the python parse failure was silently swallowed and the server started
+with servers that should have been disabled. Command and output:
+
+$ printf '{ "mcpServers": { broken\n' > /tmp/opencode/badreq/mcp-requirements.json
+$ docker run -d --name agency-spike-badreq -e OPENCODE_PASSWORD=<dummy> \
+    -e OPENCODE_API_KEY=<dummy> -v /tmp/opencode/badreq:/etc/agency:ro,z agency-base:2.0.26
+$ docker inspect -f '{{.State.ExitCode}}/{{.State.Running}}' agency-spike-badreq
+64/false
+$ docker logs agency-spike-badreq
+               ^^^^^^^^^^^^^^^^^^^^^^
+json.decoder.JSONDecodeError: Expecting property name enclosed in double quotes: line 1 column 19 (char 18)
+entrypoint: refusing to start: cannot read MCP requirements from /etc/agency/mcp-requirements.json
+
+Expected: exit code 64, not running, log names mcp-requirements.json.

images/base/entrypoint.sh

@@ -5,6 +5,8 @@
 # 3. Disable MCP servers whose required variables are unset, via an
 #    OPENCODE_CONFIG_CONTENT overlay that carries each disabled server's
 #    complete config (a later config document replaces a server entry whole).
+#    A malformed requirements file refuses to start instead of serving
+#    with servers that should have been disabled.
 # 4. Apply the fallbacks recorded under "Fallbacks in force" (none yet).
 # 5. Serve OpenCode.
 set -u
@@ -29,10 +31,12 @@ export OPENCODE_CONFIG_DIR
 
 # MCP overlay: /etc/agency/mcp-requirements.json maps each server to its
 # required variables plus its complete config. Servers with unmet
-# requirements are republished here with "disabled": true.
+# requirements are republished here with "disabled": true. A malformed
+# requirements file is a configuration error: refuse to start rather than
+# serve with servers that should have been disabled.
 req_file="/etc/agency/mcp-requirements.json"
 if [ -f "$req_file" ]; then
-  overlay=$(python3 - "$req_file" <<'PY'
+  if ! overlay=$(python3 - "$req_file" <<'PY'
 import json, os, sys
 with open(sys.argv[1]) as fh:
     req = json.load(fh)
@@ -47,7 +51,10 @@ for name, entry in req.get("mcpServers", {}).items():
 if disabled:
     print(json.dumps({"mcp": {"servers": disabled}}))
 PY
-)
+  ); then
+    echo "entrypoint: refusing to start: cannot read MCP requirements from $req_file" >&2
+    exit 64
+  fi
   if [ -n "$overlay" ]; then
     export OPENCODE_CONFIG_CONTENT="$overlay"
   fi