Prevent Phase 4 from using wrong service (ngit-relay vs ngit-grasp)

Add validation to ensure Phase 4 scripts use ngit-grasp service
(with structured logging) instead of ngit-relay service.

Changes:
- Add validate-service.sh helper for reusable service validation
- Add validation to run-migration-analysis.sh before Phase 4
- Add validation to 30-extract-parse-failures.sh
- Add validation to 31-extract-purgatory-expiry.sh
- Update migration guide with clear warnings about service selection
- Expand troubleshooting for 'Phase 4 finds no logs' issue
- Emphasize lesson learned in relay.ngit.dev notes

This prevents the issue where Phase 4 was run against ngit-relay.service
and found no parse failures because structured logging only exists in
ngit-grasp services.

4 files changed, 244 insertions, 2 deletions

diff --git a/docs/how-to/migration-scripts/30-extract-parse-failures.sh b/docs/how-to/migration-scripts/30-extract-parse-failures.sh
index bc2049a..410fcbc 100755
--- a/docs/how-to/migration-scripts/30-extract-parse-failures.sh
+++ b/docs/how-to/migration-scripts/30-extract-parse-failures.sh
@@ -65,6 +65,14 @@
 
 set -euo pipefail
 
+# Get script directory for sourcing helpers
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+
+# Source the service validation helper
+if [[ -f "$SCRIPT_DIR/validate-service.sh" ]]; then
+    source "$SCRIPT_DIR/validate-service.sh"
+fi
+
 # Colors for output (disabled if not a terminal)
 if [[ -t 1 ]]; then
     RED='\033[0;31m'
@@ -188,11 +196,35 @@ main() {
         esac
     done
     
-    # Validate service name
+    # Validate service name format
     if [[ ! "$service" =~ \.service$ ]]; then
         service="${service}.service"
     fi
     
+    # Validate service is appropriate for structured logging
+    # This prevents the common mistake of using ngit-relay instead of ngit-grasp
+    if type validate_service_for_structured_logging &>/dev/null; then
+        # Use non-interactive mode if not a terminal, skip log check (we'll do our own)
+        local interactive="true"
+        [[ ! -t 0 ]] && interactive="false"
+        
+        if ! validate_service_for_structured_logging "$service" "false" "$interactive"; then
+            log_error "Service validation failed. Use an ngit-grasp service for structured logging."
+            exit 1
+        fi
+    else
+        # Fallback validation if helper not available
+        if [[ "$service" == *"ngit-relay"* ]]; then
+            log_error "Service name appears to be ngit-relay: $service"
+            log_error "Structured logging ([PARSE_FAIL]) only exists in ngit-grasp services."
+            log_error "Please use the ngit-grasp archive service instead."
+            log_error ""
+            log_error "To find the correct service:"
+            log_error "  systemctl list-units 'ngit-grasp*' --all"
+            exit 1
+        fi
+    fi
+    
     log_info "Extracting parse failures from systemd logs"
     log_info "Service: $service"
     log_info "Output: $output_dir"
diff --git a/docs/how-to/migration-scripts/31-extract-purgatory-expiry.sh b/docs/how-to/migration-scripts/31-extract-purgatory-expiry.sh
index 8cadad9..a20780e 100755
--- a/docs/how-to/migration-scripts/31-extract-purgatory-expiry.sh
+++ b/docs/how-to/migration-scripts/31-extract-purgatory-expiry.sh
@@ -76,6 +76,14 @@
 
 set -euo pipefail
 
+# Get script directory for sourcing helpers
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+
+# Source the service validation helper
+if [[ -f "$SCRIPT_DIR/validate-service.sh" ]]; then
+    source "$SCRIPT_DIR/validate-service.sh"
+fi
+
 # Colors for output (disabled if not a terminal)
 if [[ -t 1 ]]; then
     RED='\033[0;31m'
@@ -195,11 +203,35 @@ main() {
         esac
     done
     
-    # Validate service name
+    # Validate service name format
     if [[ ! "$service" =~ \.service$ ]]; then
         service="${service}.service"
     fi
     
+    # Validate service is appropriate for structured logging
+    # This prevents the common mistake of using ngit-relay instead of ngit-grasp
+    if type validate_service_for_structured_logging &>/dev/null; then
+        # Use non-interactive mode if not a terminal, skip log check (we'll do our own)
+        local interactive="true"
+        [[ ! -t 0 ]] && interactive="false"
+        
+        if ! validate_service_for_structured_logging "$service" "false" "$interactive"; then
+            log_error "Service validation failed. Use an ngit-grasp service for structured logging."
+            exit 1
+        fi
+    else
+        # Fallback validation if helper not available
+        if [[ "$service" == *"ngit-relay"* ]]; then
+            log_error "Service name appears to be ngit-relay: $service"
+            log_error "Structured logging ([PURGATORY_EXPIRED]) only exists in ngit-grasp services."
+            log_error "Please use the ngit-grasp archive service instead."
+            log_error ""
+            log_error "To find the correct service:"
+            log_error "  systemctl list-units 'ngit-grasp*' --all"
+            exit 1
+        fi
+    fi
+    
     log_info "Extracting purgatory expiry events from systemd logs"
     log_info "Service: $service"
     log_info "Output: $output_dir"
diff --git a/docs/how-to/migration-scripts/run-migration-analysis.sh b/docs/how-to/migration-scripts/run-migration-analysis.sh
index 65d9d17..b2ca142 100755
--- a/docs/how-to/migration-scripts/run-migration-analysis.sh
+++ b/docs/how-to/migration-scripts/run-migration-analysis.sh
@@ -548,6 +548,34 @@ run_phase_4() {
         return 0
     fi
     
+    # Validate service name before running Phase 4
+    # Structured logging only exists in ngit-grasp, not ngit-relay
+    if [[ "$SERVICE_NAME" == *"ngit-relay"* ]]; then
+        log_error "SERVICE_NAME appears to be ngit-relay: $SERVICE_NAME"
+        log_error ""
+        log_error "Phase 4 requires an ngit-grasp service with structured logging."
+        log_error "Structured logging ([PARSE_FAIL], [PURGATORY_EXPIRED]) only exists"
+        log_error "in ngit-grasp services, NOT in ngit-relay services."
+        log_error ""
+        log_error "Please update --service to use the ngit-grasp archive service."
+        log_error ""
+        log_error "To find the correct service name:"
+        log_error "  systemctl list-units 'ngit-grasp*' --all"
+        log_error ""
+        log_error "Common ngit-grasp service names:"
+        log_error "  - ngit-grasp.service"
+        log_error "  - ngit-grasp-relay-ngit-dev.service (NixOS multi-instance)"
+        log_error "  - ngit-grasp-archive.service"
+        return 1
+    fi
+    
+    # Warn if service name doesn't look like ngit-grasp
+    if [[ "$SERVICE_NAME" != *"ngit-grasp"* && "$SERVICE_NAME" != *"grasp"* ]]; then
+        log_warn "SERVICE_NAME doesn't contain 'ngit-grasp': $SERVICE_NAME"
+        log_warn "Structured logging only exists in ngit-grasp services."
+        log_warn "If this is not an ngit-grasp service, Phase 4 will find no logs."
+    fi
+    
     local cmds=()
     
     cmds+=("'$SCRIPT_DIR/30-extract-parse-failures.sh' '$SERVICE_NAME' '$OUTPUT_DIR/logs'")
diff --git a/docs/how-to/migration-scripts/validate-service.sh b/docs/how-to/migration-scripts/validate-service.sh
new file mode 100755
index 0000000..2525a3f
--- /dev/null
+++ b/docs/how-to/migration-scripts/validate-service.sh
@@ -0,0 +1,150 @@
+#!/usr/bin/env bash
+#
+# validate-service.sh - Validate service name for structured logging
+#
+# This helper script validates that a service name is appropriate for
+# Phase 4 log extraction. Structured logging ([PARSE_FAIL], [PURGATORY_EXPIRED])
+# only exists in ngit-grasp services, NOT in ngit-relay services.
+#
+# USAGE:
+#   Source this script and call the validation function:
+#
+#   source validate-service.sh
+#   validate_service_for_structured_logging "$SERVICE_NAME" || exit 1
+#
+# BACKGROUND:
+#   Phase 4 of the migration analysis extracts structured log entries from
+#   journald. These log entries only exist in ngit-grasp services. If you
+#   accidentally specify an ngit-relay service, Phase 4 will find no logs
+#   and produce empty results.
+#
+#   This validation prevents that common mistake by:
+#   1. Checking if the service name contains "ngit-relay" (error)
+#   2. Warning if the service name doesn't contain "ngit-grasp"
+#   3. Optionally checking if structured logs actually exist
+#
+# SEE ALSO:
+#   docs/how-to/migrate-to-ngit-grasp.md - Full migration guide
+#   30-extract-parse-failures.sh - Uses this validation
+#   31-extract-purgatory-expiry.sh - Uses this validation
+#
+
+# Colors for output (disabled if not a terminal)
+if [[ -t 1 ]]; then
+    _VS_RED='\033[0;31m'
+    _VS_YELLOW='\033[0;33m'
+    _VS_NC='\033[0m'
+else
+    _VS_RED=''
+    _VS_YELLOW=''
+    _VS_NC=''
+fi
+
+# Validates that the service name is appropriate for structured logging
+#
+# Arguments:
+#   $1 - service_name: The systemd service name to validate
+#   $2 - check_logs: Whether to check if logs actually exist (default: "true")
+#   $3 - interactive: Whether to prompt for confirmation (default: "true")
+#
+# Returns:
+#   0 - Service is valid for structured logging
+#   1 - Service is invalid or user declined to continue
+#
+# Example:
+#   validate_service_for_structured_logging "ngit-grasp.service" || exit 1
+#   validate_service_for_structured_logging "ngit-grasp.service" "false"  # Skip log check
+#   validate_service_for_structured_logging "ngit-grasp.service" "true" "false"  # Non-interactive
+#
+validate_service_for_structured_logging() {
+    local service_name="$1"
+    local check_logs="${2:-true}"
+    local interactive="${3:-true}"
+    
+    # Check if service name looks like ngit-relay (ERROR - wrong service type)
+    if [[ "$service_name" == *"ngit-relay"* ]]; then
+        echo -e "${_VS_RED}ERROR: Service name appears to be ngit-relay: $service_name${_VS_NC}" >&2
+        echo "" >&2
+        echo "Structured logging ([PARSE_FAIL], [PURGATORY_EXPIRED]) only exists in" >&2
+        echo "ngit-grasp services, NOT in ngit-relay services." >&2
+        echo "" >&2
+        echo "Please use the ngit-grasp archive service instead." >&2
+        echo "" >&2
+        echo "To find the correct service name:" >&2
+        echo "  systemctl list-units 'ngit-grasp*' --all" >&2
+        echo "" >&2
+        echo "Common ngit-grasp service names:" >&2
+        echo "  - ngit-grasp.service" >&2
+        echo "  - ngit-grasp-relay-ngit-dev.service (NixOS multi-instance)" >&2
+        echo "  - ngit-grasp-archive.service" >&2
+        return 1
+    fi
+    
+    # Check if service name looks like ngit-grasp (WARNING if not)
+    if [[ "$service_name" != *"ngit-grasp"* && "$service_name" != *"grasp"* ]]; then
+        echo -e "${_VS_YELLOW}WARNING: Service name doesn't contain 'ngit-grasp': $service_name${_VS_NC}" >&2
+        echo "" >&2
+        echo "Structured logging ([PARSE_FAIL], [PURGATORY_EXPIRED]) only exists in" >&2
+        echo "ngit-grasp services." >&2
+        echo "" >&2
+        
+        if [[ "$interactive" == "true" ]]; then
+            read -p "Continue anyway? (y/N) " -n 1 -r
+            echo
+            if [[ ! $REPLY =~ ^[Yy]$ ]]; then
+                return 1
+            fi
+        else
+            echo "Non-interactive mode: proceeding despite warning" >&2
+        fi
+    fi
+    
+    # Optionally check if structured logs actually exist
+    if [[ "$check_logs" == "true" ]]; then
+        # Check if journalctl is available
+        if ! command -v journalctl &> /dev/null; then
+            echo -e "${_VS_YELLOW}WARNING: journalctl not available, cannot verify logs exist${_VS_NC}" >&2
+            return 0
+        fi
+        
+        # Check for structured log entries
+        local has_parse_fail has_purgatory
+        has_parse_fail=$(journalctl -u "$service_name" --since "7 days ago" 2>/dev/null | grep -c '\[PARSE_FAIL\]' || echo "0")
+        has_purgatory=$(journalctl -u "$service_name" --since "7 days ago" 2>/dev/null | grep -c '\[PURGATORY_EXPIRED\]' || echo "0")
+        
+        # Strip any non-numeric characters (grep -c can have trailing whitespace)
+        has_parse_fail="${has_parse_fail//[^0-9]/}"
+        has_purgatory="${has_purgatory//[^0-9]/}"
+        has_parse_fail="${has_parse_fail:-0}"
+        has_purgatory="${has_purgatory:-0}"
+        
+        if [[ "$has_parse_fail" -eq 0 && "$has_purgatory" -eq 0 ]]; then
+            echo -e "${_VS_YELLOW}WARNING: No structured logs found in $service_name (last 7 days)${_VS_NC}" >&2
+            echo "" >&2
+            echo "This may indicate:" >&2
+            echo "  1. Wrong service (should be ngit-grasp archive service, not ngit-relay)" >&2
+            echo "  2. Structured logging not yet deployed to this ngit-grasp instance" >&2
+            echo "  3. No parse failures or purgatory expiry events in the time window" >&2
+            echo "" >&2
+            echo "To verify you have the right service:" >&2
+            echo "  systemctl list-units 'ngit-grasp*' --all" >&2
+            echo "  journalctl -u <service> | grep -E '\\[PARSE_FAIL\\]|\\[PURGATORY_EXPIRED\\]' | head -5" >&2
+            echo "" >&2
+            
+            if [[ "$interactive" == "true" ]]; then
+                read -p "Continue anyway? (y/N) " -n 1 -r
+                echo
+                if [[ ! $REPLY =~ ^[Yy]$ ]]; then
+                    return 1
+                fi
+            else
+                echo "Non-interactive mode: proceeding despite warning" >&2
+            fi
+        fi
+    fi
+    
+    return 0
+}
+
+# Export the function so it can be used after sourcing
+export -f validate_service_for_structured_logging