diff --git a/.github/workflows/daily-pr-review-health.yml b/.github/workflows/daily-pr-review-health.yml
index 6586b3ea5..946c76aa1 100644
--- a/.github/workflows/daily-pr-review-health.yml
+++ b/.github/workflows/daily-pr-review-health.yml
@@ -100,3 +100,18 @@ jobs:
         if: env.HAS_FAILURES != 'true'
         run: |
           echo "::notice::Health check passed — all runs in the last ${LOOKBACK_DAYS} day(s) are healthy."
+
+      # Durable MCP/Context7 connectivity monitor (#903, part of #676). Asserts the
+      # handshake through the same flags engine.sh threads into its claude tiers
+      # (--mcp-config <f> --strict-mcp-config --debug mcp). No-op when MCP is
+      # unconfigured (no behavior change for non-MCP repos); fails the health check
+      # when MCP is configured but unreachable. `if: always()` keeps this monitor
+      # independent of the PR-review-failure analysis above so an MCP outage never
+      # masks (nor is masked by) that report.
+      - name: Assert MCP connectivity
+        if: always()
+        env:
+          # Reuse the #892 affirmative-diagnostics knob: a healthy handshake is
+          # surfaced as a ::notice::[mcp] success signal.
+          REVIEW_MCP_DEBUG: '1'
+        run: bash scripts/mcp_connectivity_check.sh
diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
index b079d1467..38e80a6b9 100644
--- a/.github/workflows/lint.yml
+++ b/.github/workflows/lint.yml
@@ -83,7 +83,8 @@ jobs:
             tests/test_downstream_impact_assemble.bats \
             tests/test_downstream_impact_triage_inline.bats \
             tests/test_downstream_impact_regression.bats \
-            tests/test_engine_unavailable_notice.bats
+            tests/test_engine_unavailable_notice.bats \
+            tests/test_mcp_connectivity_check.bats
 
   validate-agent-profiles:
     runs-on: ubuntu-latest
diff --git a/scripts/mcp_connectivity_check.sh b/scripts/mcp_connectivity_check.sh
new file mode 100644
index 000000000..f770e3fb9
--- /dev/null
+++ b/scripts/mcp_connectivity_check.sh
@@ -0,0 +1,202 @@
+#!/usr/bin/env bash
+# mcp_connectivity_check.sh — durable MCP/Context7 connectivity preflight (#903).
+#
+# The PR-review pipeline only surfaces MCP health as a fail-loud
+# `::warning::[mcp]` on a *real* review (engine.sh:_emit_mcp_failure_warning) —
+# a healthy run logs nothing and a silent outage is invisible until a review
+# happens to run. This script is the affirmative, durable monitor: invoked by
+# the daily health check, it drives the configured MCP server(s) through the
+# SAME flags engine.sh threads into its claude tiers
+# (`--mcp-config <f> --strict-mcp-config --debug mcp`) and asserts the handshake
+# (`MCP server "…": Successfully connected`).
+#
+# Behavior contract (mirrors the engine's opt-in MCP gating):
+#   * MCP NOT configured (no readable config) → no-op, ::notice:: skip, exit 0.
+#     Non-MCP repos see no behavior change.
+#   * MCP configured AND reachable  → ::notice::[mcp] per handshake, exit 0.
+#   * MCP configured but UNREACHABLE → ::error::[mcp], exit 1 (fails the health
+#     check). Fail Loud, Never Fake.
+#
+# Config resolution mirrors engine.sh: an explicit REVIEW_MCP_CONFIG wins; an
+# explicit empty value disables; otherwise the conventional committed path
+# (REVIEW_MCP_CONFIG_DEFAULT_PATH, default .github/review-mcp.json) is used when
+# it exists.
+#
+# Env vars consumed:
+#   REVIEW_MCP_CONFIG              — explicit config path (honored as-is; empty disables)
+#   REVIEW_MCP_CONFIG_DEFAULT_PATH — conventional fallback (default .github/review-mcp.json)
+#   REVIEW_MCP_ALLOWED_TOOLS       — explicit allowed-tools glob(s); else derived
+#                                    from the config's server names (mcp__<name>__*)
+#   MCP_PROBE_MODEL               — claude model for the probe (default claude-sonnet-4-6)
+#   MCP_PROBE_TIMEOUT_SEC         — hard timeout for the probe (default 120)
+#   CLAUDE_CODE_OAUTH_TOKEN       — passed through to the claude CLI
+
+set -euo pipefail
+
+# ---------------------------------------------------------------------------
+# Pure helpers (no network / no CLI — unit-tested in
+# tests/test_mcp_connectivity_check.bats)
+# ---------------------------------------------------------------------------
+
+# _mcp_resolve_config
+# Echoes the config path the monitor should probe, or nothing when MCP is simply
+# not configured. Precedence: explicit REVIEW_MCP_CONFIG (empty ⇒ deliberately
+# disabled) > conventional committed path when present.
+#
+# Fail-loud distinction (this is a monitor, not the graceful-degradation engine):
+#   * Unset + conventional path ABSENT → not configured → echo nothing, exit 0
+#     (no behavior change for non-MCP repos).
+#   * Explicitly pointed at a config (REVIEW_MCP_CONFIG non-empty) but the file is
+#     missing/unreadable → a misconfiguration the monitor must surface → ::error::,
+#     exit 1. Silently skipping would mask exactly the kind of silent breakage the
+#     monitor exists to catch.
+#   * Conventional path PRESENT but unreadable → same: misconfiguration → exit 1.
+_mcp_resolve_config() {
+  local default_path="${REVIEW_MCP_CONFIG_DEFAULT_PATH:-.github/review-mcp.json}"
+  if [ -n "${REVIEW_MCP_CONFIG+x}" ]; then
+    # Explicit value set (possibly empty). Empty ⇒ MCP deliberately disabled.
+    [ -z "$REVIEW_MCP_CONFIG" ] && return 0
+    if [ ! -f "$REVIEW_MCP_CONFIG" ] || [ ! -r "$REVIEW_MCP_CONFIG" ]; then
+      echo "::error::[mcp] REVIEW_MCP_CONFIG='$REVIEW_MCP_CONFIG' is set but is not a readable file" >&2
+      return 1
+    fi
+    printf '%s' "$REVIEW_MCP_CONFIG"
+    return 0
+  fi
+  # No explicit override: the conventional committed path is optional.
+  if [ -f "$default_path" ]; then
+    if [ ! -r "$default_path" ]; then
+      echo "::error::[mcp] default MCP config '$default_path' exists but is not readable" >&2
+      return 1
+    fi
+    printf '%s' "$default_path"
+  fi
+  return 0
+}
+
+# _mcp_allowed_tools <config_file>
+# Echoes the comma-separated allowed-tools glob for the probe. Honors an explicit
+# REVIEW_MCP_ALLOWED_TOOLS; otherwise derives one glob per configured server
+# (mcp__<name>__*) from the config JSON. Falls back to mcp__* if no server names
+# can be read (e.g. jq unavailable or odd shape) so the probe still permits MCP.
+_mcp_allowed_tools() {
+  local cfg="$1"
+  if [ -n "${REVIEW_MCP_ALLOWED_TOOLS:-}" ]; then
+    printf '%s' "$REVIEW_MCP_ALLOWED_TOOLS"
+    return 0
+  fi
+  local derived=""
+  if command -v jq >/dev/null 2>&1; then
+    derived="$(jq -r '(.mcpServers // {}) | keys[] | "mcp__\(.)__*"' "$cfg" 2>/dev/null \
+      | paste -sd, - || true)"
+  fi
+  printf '%s' "${derived:-mcp__*}"
+}
+
+# _mcp_failure_regex
+# Connection/init-failure regex kept in lockstep with engine.sh:_mcp_failure_pattern.
+# A degraded MCP server surfaces one of these in the CLI output even though the
+# CLI itself exits 0.
+_mcp_failure_regex() {
+  local _pat
+  _pat='mcp server [^[:space:]]*[[:space:]]*("[^"]*"[[:space:]]*)?(failed|error)'
+  _pat="$_pat"'|failed to (connect|initialize|reconnect|start)[^.]*mcp'
+  _pat="$_pat"'|mcp[^.]*(connection|initializ)[^.]*(fail|error)'
+  _pat="$_pat"'|could not (connect to|start) mcp server'
+  printf '%s' "($_pat)"
+}
+
+# _mcp_assert_connected <output_file>
+# Verdict over captured probe output (combined stdout+stderr). Emits ::notice::
+# per successful handshake and returns 0; emits ::error:: and returns 1 when a
+# failure marker is present OR no handshake line is found at all.
+_mcp_assert_connected() {
+  local out="$1"
+  [ -f "$out" ] || { echo "::error::[mcp] connectivity probe produced no output" >&2; return 1; }
+
+  if grep -qiE "$(_mcp_failure_regex)" "$out"; then
+    local servers
+    servers="$(grep -hoiE 'mcp server "[^"]+"' "$out" 2>/dev/null \
+      | sed -E 's/.*"([^"]+)".*/\1/' | sort -u | paste -sd, - || true)"
+    if [ -n "$servers" ]; then
+      echo "::error::[mcp] server(s) unreachable: ${servers} — MCP is configured (review-mcp.json) but failed to connect" >&2
+    else
+      echo "::error::[mcp] an MCP server is configured but failed to connect" >&2
+    fi
+    return 1
+  fi
+
+  local handshakes
+  handshakes="$(grep -hoiE 'mcp server "[^"]+": successfully connected.*' "$out" 2>/dev/null | sort -u || true)"
+  if [ -z "$handshakes" ]; then
+    echo "::error::[mcp] no MCP handshake observed — server is configured but did not report 'Successfully connected'" >&2
+    return 1
+  fi
+  sed 's/^/::notice::[mcp] /' <<< "$handshakes" >&2
+  return 0
+}
+
+# ---------------------------------------------------------------------------
+# main — resolves config, runs the claude probe, asserts the handshake.
+# ---------------------------------------------------------------------------
+main() {
+  local cfg
+  # Propagate a misconfiguration (unreadable/missing explicit config) as a hard
+  # failure rather than letting set -e swallow it inside the substitution.
+  cfg="$(_mcp_resolve_config)" || return 1
+  if [ -z "$cfg" ]; then
+    echo "::notice::[mcp] no MCP config present — connectivity assertion skipped (no behavior change for non-MCP repos)"
+    return 0
+  fi
+
+  local allowed_tools probe_model timeout_sec
+  allowed_tools="$(_mcp_allowed_tools "$cfg")"
+  probe_model="${MCP_PROBE_MODEL:-claude-sonnet-4-6}"
+  timeout_sec="${MCP_PROBE_TIMEOUT_SEC:-120}"
+
+  echo "=== MCP connectivity preflight ==="
+  echo "  Config:        $cfg"
+  echo "  Allowed tools: $allowed_tools"
+  echo "  Probe model:   $probe_model"
+  echo ""
+
+  local out rc=0
+  out="$(mktemp)"
+  # Clean up the capture file even if the probe is interrupted (single quotes ⇒
+  # $out is expanded when the trap fires).
+  trap 'rm -f "$out"' EXIT
+  # Same flags engine.sh threads into its MCP claude tiers, plus --debug mcp so
+  # the handshake lands in the captured output. Combine stdout+stderr; the
+  # handshake is written to stderr by `--debug mcp`. A non-zero/timeout exit is
+  # captured and folded into the assertion (a hung connect ⇒ unreachable).
+  timeout "$timeout_sec" claude --print \
+    --model "$probe_model" \
+    --no-session-persistence \
+    --max-turns 1 \
+    --mcp-config "$cfg" \
+    --strict-mcp-config \
+    --debug mcp \
+    --allowedTools "$allowed_tools" \
+    -p "MCP connectivity preflight. Reply with the single word: OK." \
+    > "$out" 2>&1 || rc=$?
+
+  if [ "$rc" -ne 0 ]; then
+    echo "::warning::[mcp] probe CLI exited non-zero (rc=$rc) — evaluating captured output for a handshake" >&2
+  fi
+
+  # Surface the captured probe output to the Actions log for diagnosis.
+  echo "--- probe output ---"
+  cat "$out"
+  echo "--- end probe output ---"
+
+  if _mcp_assert_connected "$out"; then
+    echo "MCP connectivity OK."
+    return 0
+  fi
+  return 1
+}
+
+# Only run main when executed directly (not when sourced by tests).
+if [ "${BASH_SOURCE[0]:-$0}" = "$0" ]; then
+  main "$@"
+fi
diff --git a/tests/test_mcp_connectivity_check.bats b/tests/test_mcp_connectivity_check.bats
new file mode 100644
index 000000000..b105943aa
--- /dev/null
+++ b/tests/test_mcp_connectivity_check.bats
@@ -0,0 +1,219 @@
+#!/usr/bin/env bats
+# Tests for scripts/mcp_connectivity_check.sh — the durable MCP connectivity
+# preflight (#903, part of #676).
+#
+# Verdict logic (_mcp_assert_connected) and config/tool resolution are pure and
+# tested directly. The end-to-end main() path is exercised with a stubbed
+# `claude` on PATH so no real CLI / network is needed.
+#
+# Run locally: bats tests/test_mcp_connectivity_check.bats
+
+SCRIPT_DIR="$(cd "$(dirname "$BATS_TEST_FILENAME")/.." && pwd)"
+CHECK_SCRIPT="$SCRIPT_DIR/scripts/mcp_connectivity_check.sh"
+
+setup() {
+  # shellcheck source=scripts/mcp_connectivity_check.sh
+  source "$CHECK_SCRIPT"
+
+  unset REVIEW_MCP_CONFIG REVIEW_MCP_CONFIG_DEFAULT_PATH REVIEW_MCP_ALLOWED_TOOLS
+
+  TMP="$(mktemp -d)"
+  export TMP
+
+  # A readable Context7-shaped MCP config.
+  MCP_CONFIG="$TMP/review-mcp.json"
+  cat > "$MCP_CONFIG" <<'JSON'
+{"mcpServers":{"context7":{"type":"http","url":"https://mcp.context7.com/mcp"}}}
+JSON
+
+  # Stub `claude` on PATH; behavior controlled by STUB_CLAUDE_OUT / STUB_CLAUDE_RC.
+  STUB_BIN="$TMP/bin"
+  mkdir -p "$STUB_BIN"
+  cat > "$STUB_BIN/claude" <<'STUB'
+#!/usr/bin/env bash
+printf '%s\n' "${STUB_CLAUDE_OUT:-}"
+exit "${STUB_CLAUDE_RC:-0}"
+STUB
+  chmod +x "$STUB_BIN/claude"
+  export PATH="$STUB_BIN:$PATH"
+}
+
+teardown() {
+  rm -rf "$TMP"
+  unset REVIEW_MCP_CONFIG REVIEW_MCP_CONFIG_DEFAULT_PATH REVIEW_MCP_ALLOWED_TOOLS
+  unset STUB_CLAUDE_OUT STUB_CLAUDE_RC
+}
+
+# ── _mcp_resolve_config ──────────────────────────────────────────────────────
+
+@test "resolve: explicit REVIEW_MCP_CONFIG to readable file is used" {
+  export REVIEW_MCP_CONFIG="$MCP_CONFIG"
+  run _mcp_resolve_config
+  [ "$status" -eq 0 ]
+  [ "$output" = "$MCP_CONFIG" ]
+}
+
+@test "resolve: explicit empty REVIEW_MCP_CONFIG disables (no path)" {
+  export REVIEW_MCP_CONFIG=""
+  export REVIEW_MCP_CONFIG_DEFAULT_PATH="$MCP_CONFIG"  # present but must be ignored
+  run _mcp_resolve_config
+  [ "$status" -eq 0 ]
+  [ -z "$output" ]
+}
+
+@test "resolve: no env + conventional path present → conventional path used" {
+  export REVIEW_MCP_CONFIG_DEFAULT_PATH="$MCP_CONFIG"
+  run _mcp_resolve_config
+  [ "$status" -eq 0 ]
+  [ "$output" = "$MCP_CONFIG" ]
+}
+
+@test "resolve: no env + conventional path absent → empty (MCP off)" {
+  export REVIEW_MCP_CONFIG_DEFAULT_PATH="$TMP/does-not-exist.json"
+  run _mcp_resolve_config
+  [ "$status" -eq 0 ]
+  [ -z "$output" ]
+}
+
+@test "resolve: explicit path to a missing file → fail loud (status 1 + ::error::)" {
+  export REVIEW_MCP_CONFIG="$TMP/nope.json"
+  run _mcp_resolve_config
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"::error::[mcp]"* ]]
+}
+
+@test "resolve: conventional path present but unreadable → fail loud (status 1)" {
+  [ "$(id -u)" -eq 0 ] && skip "chmod 000 is not enforced for root — readability gate is a no-op"
+  local cfg="$TMP/unreadable.json"
+  echo '{"mcpServers":{}}' > "$cfg"
+  chmod 000 "$cfg"
+  export REVIEW_MCP_CONFIG_DEFAULT_PATH="$cfg"
+  run _mcp_resolve_config
+  chmod 644 "$cfg"
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"::error::[mcp]"* ]]
+}
+
+@test "main: explicit config missing → fail loud, exit 1 (no silent skip)" {
+  export REVIEW_MCP_CONFIG="$TMP/nope.json"
+  run main
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"::error::[mcp]"* ]]
+}
+
+# ── _mcp_allowed_tools ───────────────────────────────────────────────────────
+
+@test "tools: derived from server names as mcp__<name>__*" {
+  run _mcp_allowed_tools "$MCP_CONFIG"
+  [ "$status" -eq 0 ]
+  [ "$output" = "mcp__context7__*" ]
+}
+
+@test "tools: multiple servers join comma-separated" {
+  local cfg="$TMP/multi.json"
+  echo '{"mcpServers":{"context7":{},"lsp":{}}}' > "$cfg"
+  run _mcp_allowed_tools "$cfg"
+  [ "$status" -eq 0 ]
+  [ "$output" = "mcp__context7__*,mcp__lsp__*" ]
+}
+
+@test "tools: explicit REVIEW_MCP_ALLOWED_TOOLS wins over derivation" {
+  export REVIEW_MCP_ALLOWED_TOOLS="mcp__context7__*"
+  local cfg="$TMP/multi.json"
+  echo '{"mcpServers":{"a":{},"b":{}}}' > "$cfg"
+  run _mcp_allowed_tools "$cfg"
+  [ "$status" -eq 0 ]
+  [ "$output" = "mcp__context7__*" ]
+}
+
+@test "tools: no servers in config → mcp__* fallback" {
+  local cfg="$TMP/empty.json"
+  echo '{"mcpServers":{}}' > "$cfg"
+  run _mcp_allowed_tools "$cfg"
+  [ "$status" -eq 0 ]
+  [ "$output" = "mcp__*" ]
+}
+
+# ── _mcp_assert_connected ────────────────────────────────────────────────────
+
+@test "assert: healthy handshake → ::notice::, exit 0" {
+  local out="$TMP/o"
+  printf 'MCP server "context7": Successfully connected (transport: http) in 333ms\nOK\n' > "$out"
+  run _mcp_assert_connected "$out"
+  [ "$status" -eq 0 ]
+  [[ "$output" == *"::notice::[mcp]"* ]]
+  [[ "$output" == *"context7"* ]]
+  [[ "$output" == *"Successfully connected"* ]]
+}
+
+@test "assert: failure marker → ::error:: naming server, exit 1" {
+  local out="$TMP/o"
+  printf 'MCP server "context7" failed to connect after 3 attempts\n' > "$out"
+  run _mcp_assert_connected "$out"
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"::error::[mcp]"* ]]
+  [[ "$output" == *"context7"* ]]
+}
+
+@test "assert: no handshake at all → ::error::, exit 1" {
+  local out="$TMP/o"
+  printf 'some unrelated CLI output with no mcp handshake\n' > "$out"
+  run _mcp_assert_connected "$out"
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"::error::[mcp]"* ]]
+  [[ "$output" == *"no MCP handshake"* ]]
+}
+
+@test "assert: handshake present but a later failure line → ::error:: (fail loud)" {
+  local out="$TMP/o"
+  printf 'MCP server "a": Successfully connected\nMCP server "b" failed to connect\n' > "$out"
+  run _mcp_assert_connected "$out"
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"::error::[mcp]"* ]]
+}
+
+# ── main (stubbed claude) ────────────────────────────────────────────────────
+
+@test "main: MCP unconfigured → skip notice, exit 0 (no claude call)" {
+  export REVIEW_MCP_CONFIG_DEFAULT_PATH="$TMP/does-not-exist.json"
+  run main
+  [ "$status" -eq 0 ]
+  [[ "$output" == *"::notice::[mcp]"* ]]
+  [[ "$output" == *"connectivity assertion skipped"* ]]
+}
+
+@test "main: configured + healthy handshake → exit 0" {
+  export REVIEW_MCP_CONFIG="$MCP_CONFIG"
+  export STUB_CLAUDE_OUT='MCP server "context7": Successfully connected (transport: http) in 333ms'
+  run main
+  [ "$status" -eq 0 ]
+  [[ "$output" == *"::notice::[mcp]"* ]]
+  [[ "$output" == *"MCP connectivity OK"* ]]
+}
+
+@test "main: configured but unreachable → exit 1" {
+  export REVIEW_MCP_CONFIG="$MCP_CONFIG"
+  export STUB_CLAUDE_OUT='MCP server "context7" failed to connect after 3 attempts'
+  run main
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"::error::[mcp]"* ]]
+}
+
+@test "main: configured, claude exits non-zero but handshake present → exit 0" {
+  export REVIEW_MCP_CONFIG="$MCP_CONFIG"
+  export STUB_CLAUDE_OUT='MCP server "context7": Successfully connected (transport: http) in 90ms'
+  export STUB_CLAUDE_RC=1
+  run main
+  [ "$status" -eq 0 ]
+  [[ "$output" == *"::warning::[mcp]"* ]]   # non-zero rc surfaced
+  [[ "$output" == *"MCP connectivity OK"* ]]
+}
+
+@test "main: configured, claude exits non-zero with no handshake → exit 1" {
+  export REVIEW_MCP_CONFIG="$MCP_CONFIG"
+  export STUB_CLAUDE_OUT='error: unknown flag'
+  export STUB_CLAUDE_RC=2
+  run main
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"::error::[mcp]"* ]]
+}