fix: feat: SessionStart compact hook re-injects phase protocol after context compaction (#274)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/agent-session.sh

@@ -218,6 +218,39 @@ create_agent_session() {
   fi
   rm -f "$exit_marker"
 
+  # Install SessionStart hook for context re-injection after compaction:
+  # when Claude Code compacts context during long sessions, the phase protocol
+  # instructions are lost. This hook fires after each compaction and outputs
+  # the content of a context file so Claude retains critical instructions.
+  # The context file is written by callers via write_compact_context().
+  if [ -n "$phase_file" ]; then
+    local compact_hook_script="${FACTORY_ROOT}/lib/hooks/on-compact-reinject.sh"
+    if [ -x "$compact_hook_script" ]; then
+      local context_file="${phase_file%.phase}.context"
+      local compact_hook_cmd="${compact_hook_script} ${context_file}"
+      if [ -f "$settings" ]; then
+        jq --arg cmd "$compact_hook_cmd" '
+          if (.hooks.SessionStart // [] | any(.[]; .hooks[]?.command == $cmd))
+          then .
+          else .hooks.SessionStart = (.hooks.SessionStart // []) + [{
+            matcher: "compact",
+            hooks: [{type: "command", command: $cmd}]
+          }]
+          end
+        ' "$settings" > "${settings}.tmp" && mv "${settings}.tmp" "$settings"
+      else
+        jq -n --arg cmd "$compact_hook_cmd" '{
+          hooks: {
+            SessionStart: [{
+              matcher: "compact",
+              hooks: [{type: "command", command: $cmd}]
+            }]
+          }
+        }' > "$settings"
+      fi
+    fi
+  fi
+
   # Install Stop hook for Matrix streaming: when MATRIX_THREAD_ID is set,
   # each Claude response is posted to the Matrix thread so humans can follow.
   local matrix_hook_script="${FACTORY_ROOT}/lib/hooks/on-stop-matrix.sh"
@@ -392,6 +425,16 @@ monitor_phase_loop() {
   done
 }
 
+# Write context to a file for re-injection after context compaction.
+# The SessionStart compact hook reads this file and outputs it to stdout.
+# Args: phase_file content
+write_compact_context() {
+  local phase_file="$1"
+  local content="$2"
+  local context_file="${phase_file%.phase}.context"
+  printf '%s\n' "$content" > "$context_file"
+}
+
 # Kill a tmux session gracefully (no-op if not found).
 agent_kill_session() {
   local session="${1:-}"

lib/formula-session.sh

@@ -202,6 +202,11 @@ run_formula_and_monitor() {
     exit 1
   fi
 
+  # Write phase protocol to context file for compaction survival
+  if [ -n "${PROMPT_FOOTER:-}" ]; then
+    write_compact_context "$PHASE_FILE" "$PROMPT_FOOTER"
+  fi
+
   agent_inject_into_session "$SESSION_NAME" "$PROMPT"
   log "Prompt sent to tmux session"
   matrix_send "$agent_name" "${agent_name^} session started for ${CODEBERG_REPO}" 2>/dev/null || true

lib/hooks/on-compact-reinject.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+# on-compact-reinject.sh — SessionStart (compact) hook for dark-factory agent sessions.
+#
+# Called by Claude Code after context compaction. Reads a context file and
+# outputs its content to stdout, which Claude Code injects as system context.
+# No-op if the context file doesn't exist.
+#
+# Usage (in .claude/settings.json):
+#   {"type": "command", "command": "this-script /tmp/dev-session-PROJECT-ISSUE.context"}
+#
+# Args: $1 = context file path
+
+cat > /dev/null  # consume hook JSON from stdin
+[ -n "${1:-}" ] && [ -f "$1" ] && cat "$1"
+exit 0