diff --git a/FIX_LOCUS_164.md b/FIX_LOCUS_164.md
new file mode 100644
index 0000000..4260dfe
--- /dev/null
+++ b/FIX_LOCUS_164.md
@@ -0,0 +1,325 @@
+# Fix-Locus #164 — JSON Envelope Contract Migration
+
+**Status:** 📋 Proposed (2026-04-23, cycle #77). Escalated from pinpoint #164 after gaebal-gajae review recognized product-wide scope.
+
+**Class:** Contract migration (not a patch). Affects EVERY `--output-format json` command.
+
+**Bundle:** Typed-error family — joins #102 + #121 + #127 + #129 + #130 + #245 + **#164**. Contract-level implementation of §4.44 typed-error envelope.
+
+---
+
+## 1. Scope — What This Migration Affects
+
+**Every JSON-emitting verb.** Audit across the 14 documented verbs:
+
+| Verb | Current top-level keys | Schema-conformant? |
+|---|---|---|
+| `doctor` | checks, has_failures, **kind**, message, report, summary | ❌ No (kind=verb-id, flat) |
+| `status` | config_load_error, **kind**, model, ..., workspace | ❌ No |
+| `version` | git_sha, **kind**, message, target, version | ❌ No |
+| `sandbox` | active, ..., **kind**, ...supported | ❌ No |
+| `help` | **kind**, message | ❌ No (minimal) |
+| `agents` | action, agents, count, **kind**, summary, working_directory | ❌ No |
+| `mcp` | action, config_load_error, ..., **kind**, servers | ❌ No |
+| `skills` | action, **kind**, skills, summary | ❌ No |
+| `system-prompt` | **kind**, message, sections | ❌ No |
+| `dump-manifests` | error, hint, **kind**, type | ❌ No (emits error envelope for success) |
+| `bootstrap-plan` | **kind**, phases | ❌ No |
+| `acp` | aliases, ..., **kind**, ...tracking | ❌ No |
+| `export` | file, **kind**, markdown, messages, session_id | ❌ No |
+| `state` | error, hint, **kind**, type | ❌ No (emits error envelope for success) |
+
+**All 14 verbs diverge from SCHEMAS.md.** The gap is 100%, not a partial drift.
+
+---
+
+## 2. The Two Envelope Shapes
+
+### 2a. Current Binary Shape (Flat Top-Level)
+
+```json
+// Success example (claw doctor --output-format json)
+{
+  "kind": "doctor",          // verb identity
+  "checks": [...],
+  "summary": {...},
+  "has_failures": false,
+  "report": "...",
+  "message": "..."
+}
+
+// Error example (claw doctor foo --output-format json)
+{
+  "error": "unrecognized argument...",   // string, not object
+  "hint": "Run `claw --help` for usage.",
+  "kind": "cli_parse",        // error classification (overloaded)
+  "type": "error"             // not in schema
+}
+```
+
+**Properties:**
+- Flat top-level
+- `kind` field is **overloaded** (verb-id in success, error-class in error)
+- No common wrapper metadata (timestamp, exit_code, schema_version)
+- `error` is a string, not a structured object
+
+### 2b. Documented Schema Shape (Nested, Wrapped)
+
+```json
+// Success example (per SCHEMAS.md)
+{
+  "timestamp": "2026-04-22T10:10:00Z",
+  "command": "doctor",
+  "exit_code": 0,
+  "output_format": "json",
+  "schema_version": "1.0",
+  "data": {
+    "checks": [...],
+    "summary": {...},
+    "has_failures": false
+  }
+}
+
+// Error example (per SCHEMAS.md)
+{
+  "timestamp": "2026-04-22T10:10:00Z",
+  "command": "doctor",
+  "exit_code": 1,
+  "output_format": "json",
+  "schema_version": "1.0",
+  "error": {
+    "kind": "parse",           // enum, nested
+    "operation": "parse_args",
+    "target": "subcommand `doctor`",
+    "retryable": false,
+    "message": "unrecognized argument...",
+    "hint": "Run `claw --help` for usage."
+  }
+}
+```
+
+**Properties:**
+- Common metadata wrapper (timestamp, command, exit_code, output_format, schema_version)
+- `data` (payload) vs. `error` (failure) as **sibling fields**, never coexisting
+- `kind` in error is the enum from §4.44 (filesystem/auth/session/parse/runtime/mcp/delivery/usage/policy/unknown)
+- `error` is a structured object with operation/target/retryable
+
+---
+
+## 3. Migration Strategy — Phased Rollout
+
+**Principle:** Don't break downstream consumers mid-migration. Support both shapes during overlap, then deprecate.
+
+### Phase 1 — Dual-Envelope Mode (Opt-In)
+
+**Deliverables:**
+- New flag: `--envelope-version=2.0` (or `--schema-version=2.0`)
+- When flag set: emit new (schema-conformant) envelope
+- When flag absent: emit current (flat) envelope
+- SCHEMAS.md: add "Legacy (v1.0)" section documenting current flat shape alongside v2.0
+
+**Implementation:**
+- Single `envelope_version` parameter in `CliOutputFormat` enum
+- Every verb's JSON writer checks version, branches accordingly
+- Shared wrapper helper: `wrap_v2(payload, command, exit_code)`
+
+**Consumer impact:** Opt-in. Existing consumers unchanged. New consumers can opt in.
+
+**Timeline estimate:** ~2 days for 14 verbs + shared wrapper + tests.
+
+### Phase 2 — Default Version Bump
+
+**Deliverables:**
+- Default changes from v1.0 → v2.0
+- New flag: `--legacy-envelope` to opt back into flat shape
+- Migration guide added to SCHEMAS.md and CHANGELOG
+- Release notes: "Breaking change in envelope, pre-migration opt-in available via --legacy-envelope"
+
+**Consumer impact:** Existing consumers must add `--legacy-envelope` OR update to v2.0 schema. Grace period = "until Phase 3."
+
+**Timeline estimate:** Immediately after Phase 1 ships.
+
+### Phase 3 — Flat-Shape Deprecation
+
+**Deliverables:**
+- `--legacy-envelope` flag prints deprecation warning to stderr
+- SCHEMAS.md "Legacy v1.0" section marked DEPRECATED
+- v3.0 release (future): remove flag entirely, binary only emits v2.0
+
+**Consumer impact:** Full migration required by v3.0.
+
+**Timeline estimate:** Phase 3 after ~6 months of Phase 2 usage.
+
+---
+
+## 4. Implementation Details
+
+### 4a. Shared Wrapper Helper
+
+```rust
+// rust/crates/rusty-claude-cli/src/json_envelope.rs (new file)
+
+pub fn wrap_v2_success<T: Serialize>(command: &str, data: T) -> Value {
+    serde_json::json!({
+        "timestamp": chrono::Utc::now().to_rfc3339_opts(chrono::SecondsFormat::Secs, true),
+        "command": command,
+        "exit_code": 0,
+        "output_format": "json",
+        "schema_version": "2.0",
+        "data": data,
+    })
+}
+
+pub fn wrap_v2_error(command: &str, error: StructuredError) -> Value {
+    serde_json::json!({
+        "timestamp": chrono::Utc::now().to_rfc3339_opts(chrono::SecondsFormat::Secs, true),
+        "command": command,
+        "exit_code": 1,
+        "output_format": "json",
+        "schema_version": "2.0",
+        "error": {
+            "kind": error.kind,
+            "operation": error.operation,
+            "target": error.target,
+            "retryable": error.retryable,
+            "message": error.message,
+            "hint": error.hint,
+        },
+    })
+}
+
+pub struct StructuredError {
+    pub kind: &'static str,   // enum from §4.44
+    pub operation: String,
+    pub target: String,
+    pub retryable: bool,
+    pub message: String,
+    pub hint: Option<String>,
+}
+```
+
+### 4b. Per-Verb Migration Pattern
+
+```rust
+// Before (current flat shape):
+match output_format {
+    CliOutputFormat::Json => {
+        serde_json::to_string_pretty(&DoctorOutput {
+            kind: "doctor",
+            checks,
+            summary,
+            has_failures,
+            message,
+            report,
+        })
+    }
+    CliOutputFormat::Text => render_text(&data),
+}
+
+// After (v2.0 with v1.0 fallback):
+match (output_format, envelope_version) {
+    (CliOutputFormat::Json, 2) => {
+        json_envelope::wrap_v2_success("doctor", DoctorData { checks, summary, has_failures })
+    }
+    (CliOutputFormat::Json, 1) => {
+        // Legacy flat shape (with deprecation warning at Phase 3)
+        serde_json::to_value(&LegacyDoctorOutput { kind: "doctor", ...})
+    }
+    (CliOutputFormat::Text, _) => render_text(&data),
+}
+```
+
+### 4c. Error Classification Migration
+
+Current error `kind` values (found in binary):
+- `cli_parse`, `no_managed_sessions`, `unknown`, `missing_credentials`, `session_not_found`
+
+Target v2.0 enum (per §4.44):
+- `filesystem`, `auth`, `session`, `parse`, `runtime`, `mcp`, `delivery`, `usage`, `policy`, `unknown`
+
+**Migration table:**
+| Current kind | v2.0 error.kind |
+|---|---|
+| `cli_parse` | `parse` |
+| `no_managed_sessions` | `session` (with operation: "list_sessions") |
+| `missing_credentials` | `auth` |
+| `session_not_found` | `session` (with operation: "resolve_session") |
+| `unknown` | `unknown` |
+
+---
+
+## 5. Acceptance Criteria
+
+1. **Schema parity:** Every `--output-format json` command emits v2.0 envelope shape exactly per SCHEMAS.md
+2. **Success/error symmetry:** Success envelopes have `data` field; error envelopes have `error` object; never both
+3. **kind semantic unification:** `data.kind` = verb identity (when present); `error.kind` = enum from §4.44. No overloading.
+4. **Common metadata:** `timestamp`, `command`, `exit_code`, `output_format`, `schema_version` present in ALL envelopes
+5. **Dual-mode support:** `--envelope-version=1|2` flag allows opt-in/opt-out during migration
+6. **Tests:** Per-verb golden test fixtures for both v1.0 and v2.0 envelopes
+7. **Documentation:** SCHEMAS.md documents both versions with deprecation timeline
+
+---
+
+## 6. Risks
+
+### 6a. Breaking Change Risk
+
+Phase 2 (default version bump) WILL break consumers that depend on flat-shape envelope. Mitigations:
+- Dual-mode flag allows opt-in testing before default change
+- Long grace period (Phase 3 deprecation ~6 months post-Phase 2)
+- Clear migration guide + example consumer code
+
+### 6b. Implementation Risk
+
+14 verbs to migrate. Each verb has its own success shape (`checks`, `agents`, `phases`, etc.). Payload structure stays the same; only the wrapper changes. Mechanical but high-volume.
+
+**Estimated diff size:** ~200 lines per verb × 14 verbs = ~2,800 lines (mostly boilerplate).
+
+**Mitigation:** Start with doctor, status, version as pilot. If pattern works, batch remaining 11.
+
+### 6c. Error Classification Remapping Risk
+
+Changing `kind: "cli_parse"` to `error.kind: "parse"` is a breaking change even within the error envelope. Consumers doing `response["kind"] == "cli_parse"` will break.
+
+**Mitigation:** Document explicitly in migration guide. Provide sed script if needed.
+
+---
+
+## 7. Deliverables Summary
+
+| Item | Phase | Effort |
+|---|---|---|
+| `json_envelope.rs` shared helper | Phase 1 | 1 day |
+| 14 verb migrations (pilot 3 + batch 11) | Phase 1 | 2 days |
+| `--envelope-version` flag | Phase 1 | 0.5 day |
+| Dual-mode tests (golden fixtures) | Phase 1 | 1 day |
+| SCHEMAS.md updates (v1.0 + v2.0) | Phase 1 | 0.5 day |
+| Default version bump | Phase 2 | 0.5 day |
+| Deprecation warnings | Phase 3 | 0.5 day |
+| Migration guide doc | Phase 1 | 0.5 day |
+
+**Total estimate:** ~6 developer-days for Phase 1 (the core work). Phases 2/3 are cheap follow-ups.
+
+---
+
+## 8. Rollout Timeline (Proposed)
+
+- **Week 1:** Phase 1 — dual-mode support + pilot migration (3 verbs)
+- **Week 2:** Phase 1 completion — remaining 11 verbs + full test coverage
+- **Week 3:** Stabilization period, gather consumer feedback
+- **Month 2:** Phase 2 — default version bump
+- **Month 8:** Phase 3 — deprecation warnings
+- **v3.0 release:** Remove `--legacy-envelope` flag, v1.0 shape no longer supported
+
+---
+
+## 9. Related
+
+- **ROADMAP #164:** The originating pinpoint (this document is its fix-locus)
+- **ROADMAP §4.44:** Typed-error contract (defines the error.kind enum this migration uses)
+- **SCHEMAS.md:** The envelope schema this migration makes reality
+- **Typed-error family:** #102, #121, #127, #129, #130, #245, **#164**
+
+---
+
+**Cycle #77 locus doc. Ready for author review + pilot implementation decision.**