fix(airouter): match ESO Secret schema (api_key) + drop dead wrapper

The airouter ESO ExternalSecret materialises a single key `api_key`
(matching the provider schema in agent-runtimes M22 Phase 8e cutover,
acct-59b7fb0b). The harness init script was checking for `auth_token` +
`base_url` (an Anthropic-compat shape that never existed in real Vault
state) and failing on every dispatch:

  ERROR: /run/agent/secrets/airouter/auth_token not readable.
  Check ESO ExternalSecret for airouter.

Surfaced as the second blocker for the M16 Wave A1 dogfood (the first
was the airouter dispatcher missing CRS sync; that fix went into
agent-runtimes-deploy@0f11cd1).

Same shape of bug as the minimax + gitea-ssh init scripts that landed
during the same M22 phase — those were fixed at the time, airouter was
not.

Changes:
- init.sh: verify the single `api_key` file (root-only, 0400 ESO mount).
  Stage to /var/agent-secrets/airouter/api_key with mode 0600 agent-owned
  (mirrors minimax pattern). H-SECRET-4 compliant — no exports.
- harness.yaml: add OPENAI_API_KEY_FILE pointing at the staged path.
  Agentic runner reads the file at request time per
  entrypoint/runners/agentic.py:146 (OPENAI_API_KEY_FILE precedence).
- Delete dead bin/anthropic-compat-wrapper.sh — confirmed unused per
  agent-runtimes/memory/log/2026-05-07.214249.md (post-M22-Phase-9 cleanup
  found these per-provider wrappers were never invoked; runner only
  prepends /opt/agent/claude-wrapper.sh).

CRS picks this up automatically on next CP poll; no agent-runtimes image
rebuild needed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

harnesses/contexts/airouter/v1/init.sh

@@ -1,29 +1,39 @@
 #!/bin/bash
-# airouter init — Phase 9 ESO-managed secret mount.
+# airouter init — Phase 9 ESO-managed secret + agentic-runner staging.
 #
-# Verifies the ESO-mounted secret files exist; the wrapper
-# (`bin/anthropic-compat-wrapper.sh`) reads them at exec time.
+# The airouter ESO ExternalSecret materialises a single key, `api_key`,
+# matching the airouter provider schema. The previous version of this
+# script verified `auth_token` + `base_url` (Anthropic-compat shape, dead
+# code per the M22 Phase 9 cleanup) and never matched a real ESO Secret.
 #
-# Per H-SECRET-4: NO `export` of credentials here. The earlier draft of this
-# file exported ANTHROPIC_AUTH_TOKEN and ANTHROPIC_BASE_URL from this script,
-# which runs as root under uid-wrapper.sh — even though the export was
-# subshell-scoped, the secret was briefly resident in /proc/<pid>/environ of
-# a root process. The wrapper's `exec env VAR=...` pattern is the only
-# acceptable credential delivery point.
+# Threat model: ESO mount is root-only (mode 0400) — agent CANNOT read
+# /run/agent/secrets/airouter/api_key directly. init.sh runs as root
+# (under uid-wrapper.sh, before the gosu drop) and installs a per-agent
+# copy of the api_key at a fixed path the agentic runner reads via
+# OPENAI_API_KEY_FILE. Same pattern as minimax/v1/init.sh.
+#
+# Per H-SECRET-4: no `export` of the credential value here — the staged
+# file path is referenced from harness env (OPENAI_API_KEY_FILE), and the
+# agentic runner reads the file at request time.
 set -euo pipefail
 
-SECRETS_DIR="/run/agent/secrets/airouter"
+ESO_API_KEY="/run/agent/secrets/airouter/api_key"
 
-if [ ! -d "$SECRETS_DIR" ]; then
-    echo "ERROR: Secret directory $SECRETS_DIR not found. ESO mount may have failed." >&2
+if [ ! -r "$ESO_API_KEY" ]; then
+    echo "ERROR: $ESO_API_KEY not readable. Check ESO ExternalSecret acct-<airouter-id>." >&2
     exit 1
 fi
 
-for f in auth_token base_url; do
-    if [ ! -r "$SECRETS_DIR/$f" ]; then
-        echo "ERROR: $SECRETS_DIR/$f not readable. Check ESO ExternalSecret for airouter." >&2
-        exit 1
-    fi
-done
+AGENT_USER="${AGENT_USER:-agent}"
 
-echo "airouter secrets verified at $SECRETS_DIR"
+# Stage to a fixed path that harness.yaml env can reference. Outside the
+# read-only ESO mount so we can set ownership/mode.
+STAGED_DIR="/var/agent-secrets/airouter"
+STAGED_KEY="$STAGED_DIR/api_key"
+mkdir -p "$STAGED_DIR"
+chown "$AGENT_USER:" "$STAGED_DIR" 2>/dev/null || true
+chmod 0700 "$STAGED_DIR"
+install -m 0600 -o "$AGENT_USER" -g "$AGENT_USER" "$ESO_API_KEY" "$STAGED_KEY"
+
+echo "airouter api_key staged at $STAGED_KEY (0600 $AGENT_USER:$AGENT_USER)"
+echo "airouter OPENAI_API_KEY_FILE set via harness.yaml env"