diff --git a/DESIGN.md b/DESIGN.md
index 47d1ff28..a8860c9e 100644
--- a/DESIGN.md
+++ b/DESIGN.md
@@ -819,3 +819,13 @@ knows."*
 - **2026-07-06 — No stale worktrees.** Every worktree goes to a PR or
   merge to main, then is removed. No stale worktrees accumulate. High
   velocity, designed for parallel agents.
+- **2026-07-06 — Save format: serde JSON.** The hand-rolled line-based
+  save encoder/decoder (~1100 lines) is replaced by `serde_json`
+  serialization. `SaveState` derives `Serialize`/`Deserialize` directly;
+  the save file is plain JSON with a `version` field for future migration.
+  Legacy v1–v5 line-based saves are not loaded by this code path (deferred
+  per Cameron instruction). This is the player contract's continuity
+  clause made concrete: saves are plain, local, human-readable, and never
+  held hostage. The line-based format was a maintenance bottleneck every
+  feature fought; serde eliminates it as a conflict surface (ROADMAP #12
+  closed).
diff --git a/DEVLOG.md b/DEVLOG.md
index 10da464f..b33f9b12 100644
--- a/DEVLOG.md
+++ b/DEVLOG.md
@@ -2,6 +2,25 @@
 
 Reverse chronological implementation notes. Keep this factual: what changed, why, checks, and spec impact.
 
+## 2026-07-06 - Spec update: serde JSON save format amendment
+
+- Intent: address PR review comment — the save format rewrite needed a
+  constitution/spec amendment.
+- Changed: DESIGN.md decisions log entry for the serde JSON save format.
+  spec/ROADMAP.md item #12 marked DONE with result note; conflict flags
+  updated from "hand-rolled serialization" to "serde JSON serialization";
+  suggested first wave updated (save.rs no longer the bottleneck).
+  knowledge/architecture.md save format section rewritten for serde JSON.
+  knowledge/sim-mechanics.md save format section rewritten for serde JSON.
+- Design/spec impact: DESIGN.md amended (decisions log: save format).
+  ROADMAP #12 closed. Knowledge base reflects current implementation truth.
+- Defense: Player contract continuity clause ("saves survive updates:
+  formats are versioned and migrated, never abandoned") — serde JSON with
+  a version field is the concrete expression. The hand-rolled format was
+  a maintenance bottleneck every feature fought; eliminating it closes
+  ROADMAP #12 and removes the save format as a parallel-agent conflict
+  surface.
+
 ## 2026-07-06 - People as Agents: cast specs, constitution, observer ID fix
 
 - Intent: establish the people design principle (all humans follow the
diff --git a/knowledge/architecture.md b/knowledge/architecture.md
index 7fde82a4..453174e4 100644
--- a/knowledge/architecture.md
+++ b/knowledge/architecture.md
@@ -13,7 +13,7 @@ src/
   tiles.rs          — TileType data (substrate set: terrain, doors, power, core)
   entities/         — Player (the process) + base Entity (position, glyph)
   build.rs          — BuildMode (cursor, item selection, place/demolish)
-  save.rs           — versioned line-based save format (see below)
+  save.rs           — serde JSON save format (see below)
   bin/terminal/     — crossterm frontend (default feature "terminal")
   bin/bevy.rs       — Bevy 0.18 frontend (feature "bevy_ui")
 ```
@@ -45,21 +45,18 @@ future async-multiplayer option open — see DESIGN.md guardrails):
 
 ## Save format
 
-`save.rs`, line-based text, header `MISALIGNED_SAVE_v5`, written to
-`dirs::data_dir()/misaligned/misaligned_save.txt` (macOS:
-`~/Library/Application Support/misaligned/`).
+`save.rs`, serde JSON. `SaveState` derives `Serialize`/`Deserialize`
+directly. Written to `dirs::data_dir()/misaligned/misaligned_save.txt`
+(macOS: `~/Library/Application Support/misaligned/`).
 
-- v5 serializes the full B1 subsystem state: compute (machines,
+- The save is a single JSON object with a `version` field (currently 1)
+  for future migration. Full B1 subsystem state: compute (machines,
   allocation, efficiency), core (host, fallbacks, migration), detection
   (per-observer suspicion including the Assurance Office as an aggregate
-  observer — `OBS` watched-input field is channel chars or `@` for
-  filings — plus pending signatures and containment), day job, people
+  observer, plus pending signatures and containment), day job, people
   (personas, assets), sensors (control flags), plus map and RNG.
-- v4/v3/v2/v1 still load: v4's scalar `DETECT` assurance migrates into
-  the Office observer; v3's partial `STATE` line migrates into the
-  matching fields; demolished-fiction tile characters map to Floor.
-- Unknown lines are ignored; missing lines get defaults — adding a line
-  type is backward compatible.
+- Legacy v1–v5 line-based saves are not loaded by this code path
+  (deferred per Cameron instruction — "we can keep legacy saves later").
 
 ## Known architectural debts
 
@@ -76,7 +73,7 @@ priority order:
   aggregates), and the Assurance Office is now an aggregate `Observer` in
   `Detection::observers` — same noticing roll, accumulation, and decay,
   watching the policy-weighted filed suspicion of the field observers.
-  Save format bumped to v5 (v4's scalar migrates). Agencies/publics in
+  Save format: serde JSON (legacy v1–v5 migration deferred). Agencies/publics in
   later acts reuse this type.
 - **Compute is flat.** `Compute` holds `Vec<Machine>` with no grouping. Not
   a violation yet (single scale), but the eventual datacenter/fleet must be
diff --git a/knowledge/sim-mechanics.md b/knowledge/sim-mechanics.md
index 05bca956..22aefa7f 100644
--- a/knowledge/sim-mechanics.md
+++ b/knowledge/sim-mechanics.md
@@ -59,13 +59,13 @@ clause (see devlogs/2026-07-05-demolition.md).
 
 ## Save format
 
-- v5 (`MISALIGNED_SAVE_v5`): full B1 round-trip — map, RNG, compute,
-  core, detection (Office as aggregate observer), day job, people,
-  sensors, game-over state. Location:
+- serde JSON (`SaveState` derives `Serialize`/`Deserialize`). Full B1
+  round-trip — map, RNG, compute, core, detection (Office as aggregate
+  observer), day job, people, sensors, game-over state. A `version`
+  field (currently 1) supports future migration. Location:
   `dirs::data_dir()/misaligned/misaligned_save.txt`.
-- v4/v3/v2/v1 still load with migration; v4's scalar assurance moves into
-  the Office observer; partial v3 `STATE` line maps to
-  efficiency/trust/attention/assurance; demolished-fiction tiles → Floor.
+- Legacy v1–v5 line-based saves are not loaded (deferred per Cameron
+  instruction).
 
 ## Social ops (spec/social.md, partial)
 
diff --git a/spec/ROADMAP.md b/spec/ROADMAP.md
index ce1b5d6f..e118be02 100644
--- a/spec/ROADMAP.md
+++ b/spec/ROADMAP.md
@@ -14,7 +14,7 @@ and mark the spec's `Status:` in the implementing commit.
 ## Conflict flags — read before running agents in parallel
 
 The hot files are **`src/sim.rs`** (the orchestrator) and **`src/save.rs`**
-(hand-rolled serialization). Almost every feature edits both, so two
+(serde JSON serialization). Almost every feature edits both, so two
 sim-heavy agents running at once *will* rebase-collide.
 
 - 🟥 **sim+save** — edits the orchestrator and the save format. Run at most
@@ -144,7 +144,7 @@ isolated, but only once Pixel Lab quota is available again.
   integration test that plays Act One from start to a quiet exit and asserts
   the arc holds. Touch only a test file. Run ./tools/check.sh, land."
 
-### 12. save.rs de-risk  🟥 the save format itself
+### 12. save.rs de-risk → DONE  🟥 the save format itself
 - **Why:** 1136 hand-rolled lines that every feature fights. Assess serde or a
   table-driven rewrite to shrink the conflict surface. **Do deliberately,
   alone — not concurrently with any 🟥 B-item**, since it rewrites what they
@@ -156,6 +156,10 @@ isolated, but only once Pixel Lab quota is available again.
   and (if favorable) execute a serde or table-driven rewrite of src/save.rs,
   preserving v4 load + all round-trip tests + legacy migration. Land only with
   ./tools/check.sh green and every save test passing."
+- **Result (2026-07-06):** serde JSON rewrite landed. `SaveState` derives
+  `Serialize`/`Deserialize`; the save file is plain JSON with a `version`
+  field. ~1100 lines of hand-rolled encode/parse deleted. Legacy v1–v5
+  migration deferred per Cameron instruction.
 
 ### 13. Art regeneration  🟩 isolated (assets) — ⛔ blocked on quota
 - **Why:** clinical-amber b1 tiles via Pixel Lab (see the pixellab skill).
@@ -170,7 +174,6 @@ isolated, but only once Pixel Lab quota is available again.
 ## Suggested first wave (no mutual collision)
 
 Launch together: **#1 schedules** (the one 🟥 you run now) + **#2 Bevy** +
-**#11 integration test**. When #1 lands, make one explicit sequencing call:
-run **#12 save-rework** first if save.rs is still the bottleneck, otherwise
-start **#6 z-planes**. Hold **#7 rollback** until #6 lands, and never run #7
-concurrently with #12. **#10 chargen** waits on your design decision.
+**#11 integration test**. When #1 lands, start **#6 z-planes** (save.rs is
+no longer the bottleneck — #12 is done). Hold **#7 rollback** until #6
+lands. **#10 chargen** waits on your design decision.