diff --git a/.gitignore b/.gitignore
index b67a0585..cdd34f56 100644
--- a/.gitignore
+++ b/.gitignore
@@ -41,6 +41,7 @@ sdl2-msvc/
 # Diagnostic dumps & smoke logs (transient)
 *.log
 *.jsonl
+/.aot_capture_history/
 
 # Build-generated codegen-hash header (hash_codegen.cmake): folds an emitter
 # content hash into the overlay cache path; regenerated each build, never committed.
diff --git a/docs/AOT_OVERLAY_PLAN.md b/docs/AOT_OVERLAY_PLAN.md
index e5182101..3eb87c84 100644
--- a/docs/AOT_OVERLAY_PLAN.md
+++ b/docs/AOT_OVERLAY_PLAN.md
@@ -116,6 +116,24 @@ executed_pcs[], dispatch_entry_pcs[], function_entry_pcs[], seeds[]
 (`g_dirty_ram_pc_table`, `g_dirty_ram_exec_pc_table`) — **execution-verified**, not
 disassembly guesses.
 
+#### Durable capture history (opt-in)
+
+`overlay_captures.json` remains the canonical latest snapshot consumed by the live
+compiler, but it is published through a same-directory temporary file plus atomic
+replace so readers never observe a half-written manifest. Games may additionally
+set `overlay_capture_history = true` to append each changed coherent snapshot as
+an independent JSONL record to `overlay_captures.addendum.jsonl` beside the
+executable. A hard kill can damage only the last line; the next append quarantines
+that tail, and `tools/coverage_vault.py merge --addendum ...` ignores malformed
+lines while additively merging every valid record.
+
+Development configs may also set a project-relative
+`overlay_capture_persist_dir`. This creates one atomically published, immutable
+JSON snapshot per changed capture. Absolute paths and `..` components are rejected.
+Production configs normally omit this key and retain only the naive executable-
+local addendum. Both history modes are off by default and contain game-derived
+bytes, so their outputs remain private/gitignored artifacts.
+
 ### 1.3 Compile (offline, `tools/compile_overlays.py`)
 1. Python does function-boundary discovery from the seeds (`classify_overlay_seeds`,
    `_walk_overlay_function`) with a strict callable-prologue gate; interior/
diff --git a/recompiler/src/config_loader.cpp b/recompiler/src/config_loader.cpp
index bfa105a9..77493ed0 100644
--- a/recompiler/src/config_loader.cpp
+++ b/recompiler/src/config_loader.cpp
@@ -234,6 +234,25 @@ static RuntimeConfig parse_runtime_block(const toml::value& cfg, const fs::path&
     if (runtime.contains("overlay_cache")) {
         rt.overlay_cache = toml::find<bool>(runtime, "overlay_cache");
     }
+    if (runtime.contains("overlay_capture_history")) {
+        rt.overlay_capture_history =
+            toml::find<bool>(runtime, "overlay_capture_history");
+    }
+    if (runtime.contains("overlay_capture_persist_dir")) {
+        rt.overlay_capture_persist_dir =
+            toml::find<std::string>(runtime, "overlay_capture_persist_dir");
+        const std::filesystem::path persist(rt.overlay_capture_persist_dir);
+        if (persist.is_absolute()) {
+            throw std::runtime_error(
+                "runtime.overlay_capture_persist_dir must be project-relative");
+        }
+        for (const auto& component : persist) {
+            if (component == "..") {
+                throw std::runtime_error(
+                    "runtime.overlay_capture_persist_dir must stay inside the project");
+            }
+        }
+    }
     if (runtime.contains("turbo_loads")) {
         rt.turbo_loads = toml::find<bool>(runtime, "turbo_loads");
     }
diff --git a/recompiler/src/config_loader.h b/recompiler/src/config_loader.h
index d90e1017..cdb4e114 100644
--- a/recompiler/src/config_loader.h
+++ b/recompiler/src/config_loader.h
@@ -138,6 +138,19 @@ struct RuntimeConfig {
     // overlay bytes to overlay_captures.json for offline compilation.
     bool                  overlay_cache = false;
 
+    // overlay_capture_history: opt-in durable capture history. The runtime
+    // keeps overlay_captures.json as an atomic latest snapshot for the live
+    // compiler and additionally appends every changed coherent snapshot to
+    // overlay_captures.addendum.jsonl beside the executable. A malformed tail
+    // from a hard kill cannot destroy earlier records.
+    bool                  overlay_capture_history = false;
+
+    // overlay_capture_persist_dir: optional DEV-only, project-relative safe
+    // directory for one immutable JSON file per changed snapshot. Absolute
+    // paths and `..` components are rejected. Production normally leaves this
+    // unset and retains only the addendum beside the executable.
+    std::string           overlay_capture_persist_dir;
+
     // turbo_loads: OPT-IN per game. While the game is loading (CD data
     // stream active, XA/FMV excluded, post-BIOS-handoff only) the frontend
     // skips wall-clock pacing so the guest runs at host speed — compressing
diff --git a/recompiler/tests/recompiler_patch_test.cpp b/recompiler/tests/recompiler_patch_test.cpp
index e1546e89..acfe0f64 100644
--- a/recompiler/tests/recompiler_patch_test.cpp
+++ b/recompiler/tests/recompiler_patch_test.cpp
@@ -166,6 +166,37 @@ replacement = "0x24020001"
                  "instruction-aligned", "parser rejects unaligned sites");
 }
 
+void capture_history_config_tests(const fs::path& root) {
+    const auto valid = write_config(root, "capture-history", R"toml(
+[runtime]
+overlay_cache = true
+overlay_capture_history = true
+overlay_capture_persist_dir = ".aot_capture_history/TEST-00000"
+)toml");
+    const auto cfg = PSXRecompV4::load_game_config(valid);
+    check(cfg.runtime.overlay_capture_history,
+          "parser enables durable overlay capture history");
+    check(cfg.runtime.overlay_capture_persist_dir ==
+              ".aot_capture_history/TEST-00000",
+          "parser preserves project-relative capture history directory");
+
+    const auto escaping = write_config(root, "capture-history-escape", R"toml(
+[runtime]
+overlay_capture_persist_dir = "../outside"
+)toml");
+    check_throws([&] { (void)PSXRecompV4::load_game_config(escaping); },
+                 "must stay inside the project",
+                 "parser rejects escaping capture history directory");
+
+    const auto absolute = write_config(root, "capture-history-absolute", R"toml(
+[runtime]
+overlay_capture_persist_dir = "C:/outside"
+)toml");
+    check_throws([&] { (void)PSXRecompV4::load_game_config(absolute); },
+                 "must be project-relative",
+                 "parser rejects absolute capture history directory");
+}
+
 void codegen_tests() {
     constexpr uint32_t original = 0x24020002u;    // addiu v0, zero, 2
     constexpr uint32_t replacement = 0x24020001u; // addiu v0, zero, 1
@@ -224,6 +255,7 @@ int main() {
 
     try {
         parser_tests(root);
+        capture_history_config_tests(root);
         codegen_tests();
     } catch (const std::exception& e) {
         fmt::print(stderr, "FAIL  unexpected exception: {}\n", e.what());
diff --git a/runtime/include/overlay_capture.h b/runtime/include/overlay_capture.h
index 240184c7..f2fa580c 100644
--- a/runtime/include/overlay_capture.h
+++ b/runtime/include/overlay_capture.h
@@ -32,6 +32,13 @@ void overlay_capture_init(const char *out_dir);
  * overlay_capture_on_dma() and overlay_capture_write_json() are no-ops. */
 void overlay_capture_set_enabled(int enabled);
 
+/* Opt-in durable history. When enabled, every changed coherent latest snapshot
+ * is appended to overlay_captures.addendum.jsonl beside the executable. If
+ * persist_dir is non-empty, the same snapshot is also copied atomically to one
+ * new immutable JSON file there. game_id is used only in safe filenames. */
+void overlay_capture_configure_history(int enabled, const char *persist_dir,
+                                       const char *game_id);
+
 /* Call from dma.c execute_ch3_cdrom() after every forward CH3 transfer with
  * load_start < 0x1C0000 and fntrace_is_game_started().
  * load_addr is the physical RAM destination, size is byte count,
@@ -54,6 +61,8 @@ int overlay_capture_count(void);
  * when [runtime] overlay_autocompile_cmd is configured. */
 void overlay_autocapture_set_enabled(int on);
 void overlay_autocapture_tick(void);
+/* Join any in-flight atomic writer before the final shutdown snapshot. */
+void overlay_autocapture_shutdown(void);
 void overlay_autocapture_get_status(int *enabled, uint32_t *triggers,
                                     uint64_t *last_delta);
 
diff --git a/runtime/src/main.cpp b/runtime/src/main.cpp
index 68642a3e..3e1eb0bb 100644
--- a/runtime/src/main.cpp
+++ b/runtime/src/main.cpp
@@ -978,6 +978,7 @@ static void shutdown_runtime(void) {
     /* (sljit removed 2026-07-15: overlay_compile_worker_stop joined the
      * off-thread JIT worker here; the worker no longer exists.) */
     memcard_flush_all();
+    overlay_autocapture_shutdown();
     overlay_capture_write_json();
     if (sdl_audio_device) {
         SDL_ClearQueuedAudio(sdl_audio_device);
@@ -3241,6 +3242,26 @@ int main(int argc, char** argv) {
                 std::string cache_dir = (exe_dir / "cache").string();
                 overlay_capture_set_out_dir(exe_dir.string().c_str());
                 overlay_capture_set_enabled(1);
+                std::string capture_persist_dir;
+                if (gc.runtime.overlay_capture_history &&
+                    !gc.runtime.overlay_capture_persist_dir.empty()) {
+                    std::filesystem::path persist =
+                        gc.project_root / gc.runtime.overlay_capture_persist_dir;
+                    std::error_code persist_ec;
+                    std::filesystem::create_directories(persist, persist_ec);
+                    if (persist_ec) {
+                        std::fprintf(stderr,
+                            "psxrecomp: cannot create overlay capture history %s: %s\n",
+                            persist.string().c_str(), persist_ec.message().c_str());
+                    } else {
+                        capture_persist_dir = persist.string();
+                    }
+                }
+                overlay_capture_configure_history(
+                    gc.runtime.overlay_capture_history ? 1 : 0,
+                    capture_persist_dir.empty() ? nullptr :
+                        capture_persist_dir.c_str(),
+                    game_id.c_str());
                 overlay_loader_init(cache_dir.c_str(), game_id.c_str());
                 for (uint32_t addr : gc.runtime.overlay_native_block) {
                     overlay_loader_native_block_add(addr);
diff --git a/runtime/src/overlay_capture.c b/runtime/src/overlay_capture.c
index 1cb51d10..516be488 100644
--- a/runtime/src/overlay_capture.c
+++ b/runtime/src/overlay_capture.c
@@ -6,7 +6,16 @@
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
+#include <ctype.h>
+#include <time.h>
 #include <SDL.h>
+#ifdef _WIN32
+#include <windows.h>
+#include <io.h>
+#include <process.h>
+#else
+#include <unistd.h>
+#endif
 
 /* ---- Capture set --------------------------------------------------------
  * Tracks which physical addresses have received CD DMA loads since game
@@ -34,6 +43,68 @@ static int      s_count    = 0;
 static char     s_out_dir[512];
 static int      s_active   = 0;
 static int      s_enabled  = 0;   /* config gate; off unless overlay cache enabled */
+static int      s_history_enabled = 0;
+static char     s_history_addendum[600];
+static char     s_history_persist_dir[600];
+static char     s_history_game_id[64];
+static char     s_history_session[64];
+static uint32_t s_history_sequence;
+static uint64_t s_history_last_sig;
+static int      s_history_written;
+static SDL_atomic_t s_autocap_write_state; /* 0 idle, 1 writing, 2 complete */
+
+static int capture_process_id(void)
+{
+#ifdef _WIN32
+    return _getpid();
+#else
+    return (int)getpid();
+#endif
+}
+
+static void sanitize_filename(char *dst, size_t dst_size, const char *src)
+{
+    size_t out = 0;
+    if (!dst_size) return;
+    while (src && *src && out + 1 < dst_size) {
+        unsigned char c = (unsigned char)*src++;
+        dst[out++] = (char)(isalnum(c) || c == '-' || c == '_' ? c : '_');
+    }
+    dst[out] = '\0';
+}
+
+static int sync_file(FILE *f)
+{
+    if (fflush(f) != 0) return 0;
+#ifdef _WIN32
+    return _commit(_fileno(f)) == 0;
+#else
+    return fsync(fileno(f)) == 0;
+#endif
+}
+
+static int atomic_replace_file(const char *tmp_path, const char *path)
+{
+#ifdef _WIN32
+    return MoveFileExA(tmp_path, path,
+                       MOVEFILE_REPLACE_EXISTING | MOVEFILE_WRITE_THROUGH) != 0;
+#else
+    return rename(tmp_path, path) == 0;
+#endif
+}
+
+static uint64_t capture_file_sig(const char *path)
+{
+    FILE *f = fopen(path, "rb");
+    uint64_t h = 1469598103934665603ull;
+    unsigned char buf[65536];
+    size_t n, i;
+    if (!f) return 0;
+    while ((n = fread(buf, 1, sizeof(buf), f)) > 0)
+        for (i = 0; i < n; i++) { h ^= buf[i]; h *= 1099511628211ull; }
+    fclose(f);
+    return h;
+}
 
 /* ---- Base64 encoder ----------------------------------------------------- */
 
@@ -72,6 +143,44 @@ void overlay_capture_set_enabled(int enabled)
     s_enabled = enabled ? 1 : 0;
 }
 
+void overlay_capture_configure_history(int enabled, const char *persist_dir,
+                                       const char *game_id)
+{
+    time_t now;
+    struct tm tm_now;
+    char stamp[32];
+    s_history_enabled = enabled ? 1 : 0;
+    s_history_persist_dir[0] = '\0';
+    s_history_sequence = 0;
+    s_history_last_sig = 0;
+    s_history_written = 0;
+    sanitize_filename(s_history_game_id, sizeof(s_history_game_id),
+                      game_id && game_id[0] ? game_id : "UNKNOWN");
+    if (persist_dir && persist_dir[0]) {
+        snprintf(s_history_persist_dir, sizeof(s_history_persist_dir), "%s",
+                 persist_dir);
+    }
+    snprintf(s_history_addendum, sizeof(s_history_addendum),
+             "%s/overlay_captures.addendum.jsonl", s_out_dir);
+
+    now = time(NULL);
+#ifdef _WIN32
+    gmtime_s(&tm_now, &now);
+#else
+    gmtime_r(&now, &tm_now);
+#endif
+    strftime(stamp, sizeof(stamp), "%Y%m%dT%H%M%SZ", &tm_now);
+    snprintf(s_history_session, sizeof(s_history_session), "%s-p%d",
+             stamp, capture_process_id());
+    if (s_history_enabled) {
+        fprintf(stdout,
+                "psxrecomp: durable overlay capture history enabled (%s%s%s)\n",
+                s_history_addendum,
+                s_history_persist_dir[0] ? "; immutable dir=" : "",
+                s_history_persist_dir[0] ? s_history_persist_dir : "");
+    }
+}
+
 void overlay_capture_on_dma(uint32_t load_addr, uint32_t size,
                              const uint8_t *bytes)
 {
@@ -237,17 +346,17 @@ static void write_json_window(FILE *f, uint32_t win_lo_page,
     }
 }
 
-static int write_json_snapshot(const char *path, uint32_t bw,
-                               const uint32_t *bitmap,
-                               const DirtyRamPcEntry *pc_table,
-                               const DirtyRamPcEntry *exec_pc_table,
-                               const uint8_t *ram_base)
+static int write_json_snapshot_direct(const char *path, uint32_t bw,
+                                      const uint32_t *bitmap,
+                                      const DirtyRamPcEntry *pc_table,
+                                      const DirtyRamPcEntry *exec_pc_table,
+                                      const uint8_t *ram_base)
 {
     FILE    *f;
     uint32_t page_sz;
     int      first_region;
     page_sz = 4096u;
-    f = fopen(path, "w");
+    f = fopen(path, "wb");
     if (!f) return 0;
 
     fprintf(f, "[\n");
@@ -271,10 +380,152 @@ static int write_json_snapshot(const char *path, uint32_t bw,
                       &first_region, bitmap, pc_table, exec_pc_table, ram_base);
 
     fprintf(f, "\n]\n");
-    fclose(f);
+    {
+        int ok = !ferror(f) && sync_file(f);
+        if (fclose(f) != 0) ok = 0;
+        return ok;
+    }
+}
+
+/* The live compiler needs one canonical latest snapshot, but it must never see
+ * a half-written JSON file. Format and fsync a same-directory temporary, then
+ * atomically replace the old snapshot. A hard kill leaves either the old valid
+ * file or the new valid file (plus a harmless .tmp), never a truncated latest. */
+static int write_json_snapshot_atomic(const char *path, uint32_t bw,
+                                      const uint32_t *bitmap,
+                                      const DirtyRamPcEntry *pc_table,
+                                      const DirtyRamPcEntry *exec_pc_table,
+                                      const uint8_t *ram_base)
+{
+    char tmp_path[700];
+    snprintf(tmp_path, sizeof(tmp_path), "%s.tmp-p%d", path,
+             capture_process_id());
+    if (!write_json_snapshot_direct(tmp_path, bw, bitmap, pc_table,
+                                    exec_pc_table, ram_base)) {
+        remove(tmp_path);
+        return 0;
+    }
+    if (!atomic_replace_file(tmp_path, path)) {
+        remove(tmp_path);
+        return 0;
+    }
     return 1;
 }
 
+static int copy_file_atomic(const char *src_path, const char *dst_path)
+{
+    char tmp_path[700];
+    unsigned char buf[65536];
+    FILE *src, *dst;
+    size_t n;
+    int ok = 1;
+    snprintf(tmp_path, sizeof(tmp_path), "%s.tmp-p%d", dst_path,
+             capture_process_id());
+    src = fopen(src_path, "rb");
+    if (!src) return 0;
+    dst = fopen(tmp_path, "wb");
+    if (!dst) { fclose(src); return 0; }
+    while ((n = fread(buf, 1, sizeof(buf), src)) > 0) {
+        if (fwrite(buf, 1, n, dst) != n) { ok = 0; break; }
+    }
+    if (ferror(src)) ok = 0;
+    fclose(src);
+    if (ok) ok = sync_file(dst);
+    if (fclose(dst) != 0) ok = 0;
+    if (!ok || !atomic_replace_file(tmp_path, dst_path)) {
+        remove(tmp_path);
+        return 0;
+    }
+    return 1;
+}
+
+/* Append the canonical JSON array as one minified JSONL record. Whitespace is
+ * stripped only outside strings, so bytes_b64 remains byte-for-byte intact.
+ * A crash can damage only the final line; every earlier launch remains a valid
+ * independently parseable record. */
+static int append_history_record(const char *snapshot_path, const char *reason,
+                                 uint64_t sig, uint32_t sequence)
+{
+    FILE *src = fopen(snapshot_path, "rb");
+    FILE *dst, *tail;
+    int c, in_string = 0, escape = 0, ok = 1;
+    int needs_separator = 0;
+    if (!src) return 0;
+    tail = fopen(s_history_addendum, "rb");
+    if (tail) {
+        if (fseek(tail, -1, SEEK_END) == 0) {
+            c = fgetc(tail);
+            needs_separator = c != '\n';
+        }
+        fclose(tail);
+    }
+    dst = fopen(s_history_addendum, "ab");
+    if (!dst) { fclose(src); return 0; }
+    /* Quarantine an incomplete final record from a previous hard kill. */
+    if (needs_separator && fputc('\n', dst) == EOF) ok = 0;
+    if (ok && fprintf(dst,
+            "{\"schema\":\"psxrecomp overlay capture addendum v1\","
+            "\"game\":\"%s\",\"session\":\"%s\",\"sequence\":%u,"
+            "\"reason\":\"%s\",\"fnv64\":\"%016llX\",\"captures\":",
+            s_history_game_id, s_history_session, sequence,
+            reason ? reason : "snapshot", (unsigned long long)sig) < 0) ok = 0;
+    while (ok && (c = fgetc(src)) != EOF) {
+        if (in_string) {
+            if (fputc(c, dst) == EOF) { ok = 0; break; }
+            if (escape) escape = 0;
+            else if (c == '\\') escape = 1;
+            else if (c == '"') in_string = 0;
+        } else {
+            if (c == '"') {
+                in_string = 1;
+                if (fputc(c, dst) == EOF) { ok = 0; break; }
+            } else if (!isspace((unsigned char)c)) {
+                if (fputc(c, dst) == EOF) { ok = 0; break; }
+            }
+        }
+    }
+    if (ferror(src) || in_string) ok = 0;
+    fclose(src);
+    if (ok && fprintf(dst, "}\n") < 0) ok = 0;
+    if (ok) ok = sync_file(dst);
+    if (fclose(dst) != 0) ok = 0;
+    return ok;
+}
+
+static void persist_history_snapshot(const char *snapshot_path,
+                                     const char *reason, uint64_t sig)
+{
+    char persist_path[800];
+    uint32_t sequence;
+    int addendum_saved;
+    int persist_saved = s_history_persist_dir[0] ? 0 : 1;
+    if (!s_history_enabled || !sig) return;
+    if (s_history_written && sig == s_history_last_sig) return;
+    sequence = ++s_history_sequence;
+
+    if (s_history_persist_dir[0]) {
+        snprintf(persist_path, sizeof(persist_path),
+                 "%s/%s_%s_%04u_%016llX.json",
+                 s_history_persist_dir, s_history_game_id, s_history_session,
+                 sequence, (unsigned long long)sig);
+        if (copy_file_atomic(snapshot_path, persist_path)) persist_saved = 1;
+        else fprintf(stderr,
+            "psxrecomp: failed to persist overlay capture snapshot %s\n",
+            persist_path);
+    }
+    addendum_saved = append_history_record(snapshot_path, reason, sig, sequence);
+    if (!addendum_saved)
+        fprintf(stderr, "psxrecomp: failed to append overlay capture history %s\n",
+                s_history_addendum);
+    /* Retry an unchanged snapshot if either configured durable sink failed.
+     * Repeated addendum records or immutable files are harmless: vault merges
+     * are content-keyed and idempotent. */
+    if (addendum_saved && persist_saved) {
+        s_history_last_sig = sig;
+        s_history_written = 1;
+    }
+}
+
 void overlay_capture_write_json(void)
 {
     extern uint8_t *memory_get_ram_ptr(void);
@@ -282,12 +533,18 @@ void overlay_capture_write_json(void)
     uint32_t bw = dirty_ram_get_bitmap_word_count();
     uint32_t *bitmap;
     if (!s_active) return;
+    /* Manual dumps do not race the periodic worker. Shutdown joins it first. */
+    if (SDL_AtomicGet(&s_autocap_write_state) != 0) return;
     bitmap = (uint32_t *)malloc((size_t)bw * sizeof(uint32_t));
     if (!bitmap) return;
     for (uint32_t i = 0; i < bw; i++) bitmap[i] = dirty_ram_get_bitmap_word(i);
     snprintf(path, sizeof(path), "%s/overlay_captures.json", s_out_dir);
-    write_json_snapshot(path, bw, bitmap, g_dirty_ram_pc_table,
-                        g_dirty_ram_exec_pc_table, memory_get_ram_ptr());
+    if (write_json_snapshot_atomic(path, bw, bitmap, g_dirty_ram_pc_table,
+                                   g_dirty_ram_exec_pc_table,
+                                   memory_get_ram_ptr())) {
+        uint64_t sig = capture_file_sig(path);
+        persist_history_snapshot(path, "shutdown-or-manual", sig);
+    }
     free(bitmap);
 }
 
@@ -355,9 +612,9 @@ typedef struct {
     uint32_t *bitmap;
     uint32_t bitmap_words;
     uint64_t manifest_sig;
+    int write_ok;
     char path[600];
 } AutocapWriteJob;
-static SDL_atomic_t s_autocap_write_state; /* 0 idle, 1 writing, 2 complete */
 static SDL_Thread *s_autocap_write_thread;
 static AutocapWriteJob *s_autocap_write_job;
 static int s_autocap_seeded_existing;
@@ -401,17 +658,8 @@ void overlay_autocapture_get_futility(uint32_t *backoff, uint32_t *futile) {
 static uint64_t autocap_manifest_sig(void)
 {
     char path[600];
-    FILE *f;
-    uint64_t h = 1469598103934665603ull;
-    unsigned char buf[65536];
-    size_t n, i;
     snprintf(path, sizeof(path), "%s/overlay_captures.json", s_out_dir);
-    f = fopen(path, "rb");
-    if (!f) return 0;
-    while ((n = fread(buf, 1, sizeof(buf), f)) > 0)
-        for (i = 0; i < n; i++) { h ^= buf[i]; h *= 1099511628211ull; }
-    fclose(f);
-    return h;
+    return capture_file_sig(path);
 }
 
 static void autocap_write_job_free(AutocapWriteJob *job)
@@ -425,9 +673,14 @@ static int autocap_write_thread_main(void *opaque)
 {
     AutocapWriteJob *job = (AutocapWriteJob *)opaque;
     SDL_SetThreadPriority(SDL_THREAD_PRIORITY_LOW);
-    if (write_json_snapshot(job->path, job->bitmap_words, job->bitmap,
-                            job->pc_table, job->exec_pc_table, job->ram))
-        job->manifest_sig = autocap_manifest_sig();
+    job->write_ok = write_json_snapshot_atomic(
+        job->path, job->bitmap_words, job->bitmap,
+        job->pc_table, job->exec_pc_table, job->ram);
+    if (job->write_ok) {
+        job->manifest_sig = capture_file_sig(job->path);
+        persist_history_snapshot(job->path, "autocap",
+                                 job->manifest_sig);
+    }
     SDL_AtomicSet(&s_autocap_write_state, 2);
     return 0;
 }
@@ -531,6 +784,22 @@ void overlay_autocapture_tick(void)
     autocap_write_start();
 }
 
+void overlay_autocapture_shutdown(void)
+{
+    int state = SDL_AtomicGet(&s_autocap_write_state);
+    if (state == 0) return;
+    if (s_autocap_write_thread) {
+        SDL_WaitThread(s_autocap_write_thread, NULL);
+        s_autocap_write_thread = NULL;
+    }
+    /* The worker atomically published and durably archived the coherent
+     * snapshot before setting state=2. No compiler request is needed while
+     * shutting down; just release its copied inputs before the final snapshot. */
+    autocap_write_job_free(s_autocap_write_job);
+    s_autocap_write_job = NULL;
+    SDL_AtomicSet(&s_autocap_write_state, 0);
+}
+
 uint32_t overlay_capture_get_region_crc(uint32_t region_start,
                                          uint32_t region_size)
 {
diff --git a/runtime/tests/test_capture_history.py b/runtime/tests/test_capture_history.py
new file mode 100644
index 00000000..4d43578e
--- /dev/null
+++ b/runtime/tests/test_capture_history.py
@@ -0,0 +1,64 @@
+#!/usr/bin/env python3
+"""Regression checks for append-only overlay capture history ingestion."""
+import importlib.util
+import json
+import pathlib
+import tempfile
+
+
+ROOT = pathlib.Path(__file__).resolve().parents[2]
+SPEC = importlib.util.spec_from_file_location(
+    "coverage_vault", ROOT / "tools" / "coverage_vault.py")
+MOD = importlib.util.module_from_spec(SPEC)
+assert SPEC.loader is not None
+SPEC.loader.exec_module(MOD)
+
+
+def region(addr, payload, pcs):
+    return {
+        "schema": "psxrecomp overlay capture v2",
+        "load_addr": addr,
+        "size": 4,
+        "bytes_b64": payload,
+        "executed_pcs": pcs,
+        "dispatch_entry_pcs": pcs,
+        "function_entry_pcs": [],
+        "seeds": pcs,
+    }
+
+
+def main():
+    with tempfile.TemporaryDirectory() as td:
+        root = pathlib.Path(td)
+        addendum = root / "overlay_captures.addendum.jsonl"
+        vault = root / "vault" / "overlay_captures.json"
+        first = region("0x80100000", "AAAAAA==", ["0x80100000"])
+        second = region("0x80100000", "AQAAAA==", ["0x80100004"])
+        records = [
+            {"schema": "psxrecomp overlay capture addendum v1",
+             "captures": [first]},
+            {"schema": "psxrecomp overlay capture addendum v1",
+             "captures": [first, second]},
+        ]
+        with addendum.open("w", encoding="utf-8", newline="\n") as out:
+            out.write(json.dumps(records[0], separators=(",", ":")) + "\n")
+            # A later launch first quarantines a hard-killed partial record.
+            out.write('{"schema":"torn-tail"\n')
+            out.write(json.dumps({"schema": "unrelated", "captures": [second]},
+                                 separators=(",", ":")) + "\n")
+            out.write(json.dumps(records[1], separators=(",", ":")) + "\n")
+
+        new_variants, new_pcs = MOD.merge_addendum(str(vault), str(addendum))
+        assert new_variants == 2
+        assert new_pcs == 2
+        merged = json.loads(vault.read_text(encoding="utf-8"))
+        assert len(merged) == 2
+        assert not list(vault.parent.glob("*.tmp-*"))
+
+        # Re-ingesting the same durable history is additive and idempotent.
+        assert MOD.merge_addendum(str(vault), str(addendum)) == (0, 0)
+        print("ALL PASS")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/tools/aot_overlay_spike/README.md b/tools/aot_overlay_spike/README.md
index 296aded4..65aa210c 100644
--- a/tools/aot_overlay_spike/README.md
+++ b/tools/aot_overlay_spike/README.md
@@ -43,6 +43,24 @@ A mis-positioned / data-as-code shard either fails audit at compile time or neve
 fires at runtime → coverage loss, never incorrect execution. Whatever static
 misses, production autocompile (tcc/gcc) self-heals on first visit.
 
+## Durable runtime capture history
+
+The canonical `overlay_captures.json` is atomically replaced for live consumers.
+With `[runtime] overlay_capture_history = true`, each changed coherent snapshot is
+also appended as one independent record to
+`overlay_captures.addendum.jsonl` beside the executable. A torn final line does
+not invalidate earlier or later records. Merge it into the private additive vault
+with:
+
+```sh
+python tools/coverage_vault.py merge --vault <vault-dir> \
+  --addendum <exe-dir>/overlay_captures.addendum.jsonl
+```
+
+Dev configs can additionally set the project-relative
+`overlay_capture_persist_dir` to retain immutable per-snapshot JSON files. Both
+settings are opt-in; capture artifacts contain game bytes and must stay ignored.
+
 ## Multi-game sweep findings (2026-07-17)
 
 `extract_generic.py` runs the improved extraction from a game.toml. Results:
diff --git a/tools/coverage_vault.py b/tools/coverage_vault.py
index 929a8c04..22c9bda6 100644
--- a/tools/coverage_vault.py
+++ b/tools/coverage_vault.py
@@ -19,7 +19,8 @@ It contains game-derived bytes, so the vault dir must stay gitignored / private
 and is committed.
 
 Usage:
-  coverage_vault.py merge --vault DIR [--captures captures.json] [--cache CACHE_DIR]
+  coverage_vault.py merge --vault DIR [--captures captures.json]
+                          [--addendum captures.addendum.jsonl] [--cache CACHE_DIR]
   coverage_vault.py stats --vault DIR
 """
 import argparse, json, os, shutil, hashlib, sys
@@ -35,16 +36,58 @@ def _load_list(path):
     if not os.path.exists(path):
         return []
     try:
-        v = json.load(open(path, encoding="utf-8"))
-        return v if isinstance(v, list) else []
+        with open(path, encoding="utf-8") as source:
+            value = json.load(source)
+        return value if isinstance(value, list) else []
     except Exception as e:
         print("  warn: could not read %s (%s); starting fresh" % (path, e))
         return []
 
-def merge_captures(vault_json, src_json):
-    if not src_json or not os.path.exists(src_json):
-        return 0, 0
-    src = _load_list(src_json)
+def _load_addendum(path):
+    """Load every valid append-only history record, ignoring a torn tail.
+
+    Each line is an independent snapshot wrapper. A hard kill may truncate only
+    the final line; earlier launches remain usable and a later runtime append
+    quarantines the bad tail with a newline.
+    """
+    regions = []
+    if not path or not os.path.exists(path):
+        return regions
+    with open(path, encoding="utf-8", errors="replace") as history:
+        for lineno, line in enumerate(history, 1):
+            if not line.strip():
+                continue
+            try:
+                record = json.loads(line)
+            except Exception as e:
+                print("  warn: ignoring invalid addendum line %d in %s (%s)" %
+                      (lineno, path, e))
+                continue
+            if not isinstance(record, dict) or record.get("schema") != (
+                    "psxrecomp overlay capture addendum v1"):
+                print("  warn: ignoring unknown addendum record on line %d in %s" %
+                      (lineno, path))
+                continue
+            captures = record.get("captures", [])
+            if isinstance(captures, list):
+                regions.extend(r for r in captures if isinstance(r, dict))
+    return regions
+
+def _write_list_atomic(path, value):
+    os.makedirs(os.path.dirname(path) or ".", exist_ok=True)
+    tmp = "%s.tmp-%d" % (path, os.getpid())
+    try:
+        with open(tmp, "w", encoding="utf-8", newline="\n") as out:
+            json.dump(value, out, indent=1)
+            out.write("\n")
+            out.flush()
+            os.fsync(out.fileno())
+        os.replace(tmp, path)
+    finally:
+        if os.path.exists(tmp):
+            os.unlink(tmp)
+
+def merge_capture_regions(vault_json, src):
     if not src:
         return 0, 0
     index = { _variant_key(r): r for r in _load_list(vault_json) }
@@ -63,10 +106,17 @@ def merge_captures(vault_json, src_json):
                 if fld == "executed_pcs":
                     new_pcs += len(add - cur)
                 tgt[fld] = sorted(cur | add)
-    os.makedirs(os.path.dirname(vault_json) or ".", exist_ok=True)
-    json.dump(list(index.values()), open(vault_json, "w", encoding="utf-8"), indent=1)
+    _write_list_atomic(vault_json, list(index.values()))
     return new_variants, new_pcs
 
+def merge_captures(vault_json, src_json):
+    if not src_json or not os.path.exists(src_json):
+        return 0, 0
+    return merge_capture_regions(vault_json, _load_list(src_json))
+
+def merge_addendum(vault_json, addendum):
+    return merge_capture_regions(vault_json, _load_addendum(addendum))
+
 def merge_cache(vault_cache, src_cache):
     """Mirror compiled DLLs/.ranges into the vault, PRESERVING the relative
     layout (<compiler>/<arch-abi>/cg<N>_<hash>/file). The layout is load-
@@ -111,6 +161,7 @@ def main():
     ap.add_argument("cmd", choices=["merge", "stats"])
     ap.add_argument("--vault", required=True, help="vault directory (kept gitignored/private)")
     ap.add_argument("--captures", help="source overlay_captures.json to merge in")
+    ap.add_argument("--addendum", help="append-only overlay capture history (.jsonl)")
     ap.add_argument("--cache", help="source cache dir (e.g. build/cache/<game_id>) to merge in")
     a = ap.parse_args()
     if a.cmd == "stats":
@@ -118,7 +169,13 @@ def main():
         return 0
     vj = os.path.join(a.vault, CAP_NAME)
     vc = os.path.join(a.vault, CACHE_SUB)
-    nv, np_ = merge_captures(vj, a.captures) if a.captures else (0, 0)
+    nv = np_ = 0
+    if a.captures:
+        add_v, add_p = merge_captures(vj, a.captures)
+        nv += add_v; np_ += add_p
+    if a.addendum:
+        add_v, add_p = merge_addendum(vj, a.addendum)
+        nv += add_v; np_ += add_p
     nd = merge_cache(vc, a.cache) if a.cache else 0
     print("coverage_vault: +%d new variant(s), +%d new PC(s), +%d new DLL(s) -> %s" % (nv, np_, nd, a.vault))
     return 0