fix(minimax): wire api_key via apiKeyHelper, never via env

Mirrors agent-runtimes commit 1b83c81. CRS serves these harness files
to dispatchers, so this repo must match for the fix to take effect.

The minimax harness now writes ~/.claude/settings.json with an
apiKeyHelper that `cat`s the ESO-mounted /run/agent/secrets/minimax/
api_key file. Claude Code routes apiKeyHelper output to
`Authorization: Bearer <value>` for non-anthropic.com base URLs, which
is what MiniMax's /anthropic proxy requires. The secret is never read
into env, never written into a config file, and ESO rotation is
auto-recovered via Claude Code's per-session helper invocation
(also re-runs after a 401).

- harness.yaml: drop ANTHROPIC_AUTH_TOKEN_FILE env var
- init.sh: write (or jq-merge) settings.json with apiKeyHelper, chmod 0600
- bin/anthropic-compat-wrapper.sh: deleted

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

harnesses/contexts/minimax/v1/bin/anthropic-compat-wrapper.sh

@@ -1,9 +0,0 @@
-#!/bin/bash
-# Anthropic-compat wrapper for MiniMax (Phase 9 ESO-managed secrets).
-# Reads the api_key file and passes it as ANTHROPIC_AUTH_TOKEN to claude.
-# ANTHROPIC_BASE_URL is set in harness.yaml `env:` and flows through.
-set -euo pipefail
-
-exec env \
-  ANTHROPIC_AUTH_TOKEN="$(cat /run/agent/secrets/minimax/api_key)" \
-  claude "$@"

harnesses/contexts/minimax/v1/harness.yaml

@@ -5,9 +5,11 @@ description: "MiniMax coding plan — Anthropic-compatible proxy"
 requires: []
 provides: [claude-code]
 
+# Auth is wired by init.sh via Claude Code's apiKeyHelper (settings.json).
+# No credential env vars: the secret stays in the mounted file and is read
+# only by the helper command at request time.
 env:
   ANTHROPIC_BASE_URL: "https://api.minimax.io/anthropic"
-  ANTHROPIC_AUTH_TOKEN_FILE: "/run/agent/secrets/minimax/api_key"
   CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS: "1"
   CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC: "1"
   DISABLE_PROMPT_CACHING: "1"

harnesses/contexts/minimax/v1/init.sh

@@ -1,12 +1,24 @@
 #!/bin/bash
-set -euo pipefail
-
-# Verify the ESO-managed MiniMax api_key file is mounted. The wrapper
-# (`bin/anthropic-compat-wrapper.sh`) reads it at exec time and exports
-# ANTHROPIC_AUTH_TOKEN to the claude subprocess.
+# minimax init — write ~/.claude/settings.json with apiKeyHelper.
 #
-# ANTHROPIC_BASE_URL is set in harness.yaml `env:` (not in the K8s Secret),
-# so no file check is required for it.
+# The MiniMax API key is mounted by ESO at /run/agent/secrets/minimax/api_key
+# (mode 0400, secrets_required entry in harness.yaml). Claude Code's
+# `apiKeyHelper` setting names a command that prints the key on stdout when
+# the CLI needs it for an API request — the value never enters this process'
+# environment, never appears in /proc/<pid>/environ of the claude subprocess,
+# and is read fresh on each invocation so ESO secret rotations are picked up
+# without a process restart.
+#
+# Why settings.json (not --settings inline or env vars):
+#  - ANTHROPIC_AUTH_TOKEN / ANTHROPIC_API_KEY in env exposes the secret in
+#    /proc/<pid>/environ, log aggregators, ps. The H-SECRET-4 rule disallows
+#    credential-shaped env vars for that reason.
+#  - --settings on the runner CLI line couples the runner to the harness
+#    layout. Per-harness settings.json keeps auth a harness concern.
+#  - The helper command (`cat <file>`) re-reads on each call, so secret
+#    rotation propagates without rewriting the config file.
+
+set -euo pipefail
 
 API_KEY_FILE="/run/agent/secrets/minimax/api_key"
 
@@ -15,4 +27,30 @@ if [ ! -r "$API_KEY_FILE" ]; then
     exit 1
 fi
 
-echo "minimax api_key verified at $API_KEY_FILE"
+# Resolve the agent's home and write settings.json there. CLAUDE_CONFIG_DIR
+# overrides ~/.claude when set; honour it so non-default profiles work.
+CONFIG_DIR="${CLAUDE_CONFIG_DIR:-$HOME/.claude}"
+mkdir -p "$CONFIG_DIR"
+chmod 0700 "$CONFIG_DIR"
+
+SETTINGS_FILE="$CONFIG_DIR/settings.json"
+
+# If a settings.json already exists from another harness layer, merge
+# apiKeyHelper into it; otherwise create a minimal file. jq is in the base
+# image; fall back to a clean overwrite if it isn't available for any reason.
+if [ -f "$SETTINGS_FILE" ] && command -v jq >/dev/null 2>&1; then
+    TMP=$(mktemp)
+    jq --arg helper "cat $API_KEY_FILE" \
+       '. + {apiKeyHelper: $helper}' \
+       "$SETTINGS_FILE" > "$TMP"
+    mv "$TMP" "$SETTINGS_FILE"
+else
+    cat > "$SETTINGS_FILE" <<EOF
+{
+  "apiKeyHelper": "cat $API_KEY_FILE"
+}
+EOF
+fi
+
+chmod 0600 "$SETTINGS_FILE"
+echo "minimax api_key wired via apiKeyHelper at $SETTINGS_FILE"