diff --git a/docs/agent-constraints.md b/docs/agent-constraints.md
index 1e6754b..7a9f9c5 100644
--- a/docs/agent-constraints.md
+++ b/docs/agent-constraints.md
@@ -37,6 +37,11 @@ It is distinct from `docs/requirements-log.md`, which records **project/product
    - Keep `workflow/session-handover.md` updated with a same-day entry for the active branch.
    - If the check fails, stop and fix handover artifacts first.
 
+6. **Process-change-first execution gate**
+   - If process/governance change is required, merge the process ticket to the feature branch first.
+   - Do not start code/test edits for implementation tickets until process merge evidence is confirmed.
+   - Subagents must be constrained to read-only exploration until the process gate is satisfied.
+
 ## Change Control
 
 - Changes to this file follow the same workflow as code changes.
@@ -56,3 +61,9 @@ It is distinct from `docs/requirements-log.md`, which records **project/product
 - All agents must pre-read `docs/commands.md` and `docs/workflow.md` troubleshooting before running Gitea issue/PR/comment commands.
 - `gh` CLI is prohibited for repository ticket/PR operations; use `tea` (or documented Gitea API fallback only).
 - Session start must pass `python3 scripts/session_handover_check.py --strict`, with branch-matched entry in `workflow/session-handover.md`.
+
+### 2026-02-27
+
+- Apply process-change-first as an execution gate: process ticket must be merged before implementation ticket coding.
+- Handover entry must record concrete `next_ticket` and `process_gate_checked`; placeholders are not allowed in strict gate.
+- Before process merge confirmation, all subagent tasks must remain read-only (analysis only).
diff --git a/docs/workflow.md b/docs/workflow.md
index d8ba052..1b07639 100644
--- a/docs/workflow.md
+++ b/docs/workflow.md
@@ -188,6 +188,19 @@ Use `run_in_background=True` for independent tasks that don't block subsequent w
 - process ticket 미반영 상태에서 기능 티켓 코딩/머지 금지
 - 세션 전환 시에도 동일 규칙 유지
 
+### Implementation Start Gate (Mandatory)
+
+구현 티켓을 시작하기 전에 아래 3개를 모두 만족해야 한다.
+
+1. `process ticket merge` 증적 확인 (feature branch 반영 커밋/PR)
+2. `workflow/session-handover.md` 최신 엔트리에 `next_ticket`과 `process_gate_checked` 기록
+3. `python3 scripts/session_handover_check.py --strict` 통과
+
+강제 규칙:
+- 위 3개 중 하나라도 불충족이면 코드/테스트 수정 금지
+- 서브에이전트 지시도 동일하게 제한한다 (`process merged 확인 전 read-only 탐색만 허용`)
+- 성급 착수 발견 시 구현 작업을 즉시 중단하고 handover/proces gate부터 복구한다
+
 ### Ticket Maturity Stages (Mandatory)
 
 모든 티켓은 아래 4단계를 순서대로 통과해야 한다.
diff --git a/scripts/session_handover_check.py b/scripts/session_handover_check.py
index 229301e..b2ded16 100755
--- a/scripts/session_handover_check.py
+++ b/scripts/session_handover_check.py
@@ -81,6 +81,7 @@ def _check_handover_entry(
         "- docs_checked:",
         "- open_issues_reviewed:",
         "- next_ticket:",
+        "- process_gate_checked:",
     )
     for token in required_tokens:
         if token not in latest:
@@ -98,6 +99,13 @@ def _check_handover_entry(
                 "latest handover entry must target current branch "
                 f"({branch_token})"
             )
+        if "- next_ticket: #TBD" in latest:
+            errors.append("latest handover entry must not use placeholder next_ticket (#TBD)")
+        if "merged_to_feature_branch=no" in latest:
+            errors.append(
+                "process gate indicates not merged; implementation must stay blocked "
+                "(merged_to_feature_branch=no)"
+            )
 
 
 def main() -> int:
diff --git a/workflow/session-handover.md b/workflow/session-handover.md
index 4233291..68085f6 100644
--- a/workflow/session-handover.md
+++ b/workflow/session-handover.md
@@ -15,6 +15,7 @@
 - docs_checked: docs/workflow.md, docs/commands.md, docs/agent-constraints.md
 - open_issues_reviewed: #...
 - next_ticket: #...
+- process_gate_checked: process_ticket=#..., merged_to_feature_branch=yes|no|n/a
 - risks_or_notes: ...
 ```
 
@@ -24,3 +25,19 @@
 - open_issues_reviewed: #304, #305, #306
 - next_ticket: #304
 - risks_or_notes: 세션 시작 게이트를 문서/스크립트/CI로 강제 적용
+
+### 2026-02-27 | session=codex-handover-start
+- branch: feature/v3-session-policy-stream
+- docs_checked: docs/workflow.md, docs/commands.md, docs/agent-constraints.md
+- open_issues_reviewed: #306, #308, #309
+- next_ticket: #304
+- process_gate_checked: process_ticket=#306,#308 merged_to_feature_branch=yes
+- risks_or_notes: 미추적 로컬 파일 존재(문서/DB/lock)로 커밋 범위 분리 필요
+
+### 2026-02-27 | session=codex-process-gate-hardening
+- branch: feature/issue-304-runtime-staged-exit-semantics
+- docs_checked: docs/workflow.md, docs/commands.md, docs/agent-constraints.md
+- open_issues_reviewed: #304, #305
+- next_ticket: #304
+- process_gate_checked: process_ticket=#306,#308 merged_to_feature_branch=yes
+- risks_or_notes: process-change-first 실행 게이트를 문서+스크립트로 강화