chore: add icon.ico so the exe gets the proper program icon

thor-watcher had no icon.ico, so build.bat's 'if exist icon.ico' check
always fell through to building without --icon → PyInstaller's default
Python/floppy icon. Reuse the shared Terra-Mechanics icon from
series3-watcher; build.bat now picks it up automatically (no script
change needed). Rides with the pending 0.4.1 build.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -5,6 +5,38 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.4.1] - 2026-06-25
+
+### Fixed
+- **Auto-updater no longer dies when settings are saved.** Saving the Settings dialog restarts the watcher thread via `_restart_watcher`, which sets and then replaces the shared `stop_event`. Because the updater loop keyed off that *same* event, saving settings would terminate the auto-updater thread (a race — it could survive one save and die on the next). The watcher kept running and reporting heartbeats normally, but the agent silently stopped checking for / applying updates until the tray app was relaunched. The updater now keys off its own app-lifetime event (`_app_stop`) that watcher restarts never touch; it stops only on Exit or when applying an update.
+- Added `test_thor_tray.py` covering the tray thread lifecycle (updater survives a watcher restart; stops on app exit; `_exit`/`_do_update` signal the lifetime event).
+
+## [0.4.0] - 2026-06-25
+
+### Added — Mirror (dual-send)
+- **Optional best-effort mirror server.** Each heartbeat and each forwarded event can now be sent to a *second* ("mirror") server in addition to the primary, so a standby box (e.g. the office NAS) stays a continuous replica during a migration — making the eventual cutover a non-event. **Default off** — blank `mirror_api_url`/`mirror_sfm_url` means existing installs are unchanged after auto-update.
+- **Heartbeat mirror (best-effort).** After the primary heartbeat POST, the same payload is fired at `mirror_api_url` when set. Bounded by the existing API timeout and fully wrapped — it can never delay or fail the primary heartbeat; its result is ignored except for a debug log line.
+- **Event mirror (reliable, isolated).** Events are re-forwarded to `mirror_sfm_url` using a *separate* sha256 state file (`mirror_sfm_state_file`, blank → `<log_dir>/thor_forwarded_mirror.json`), so the mirror tracks its own delivery independently of the primary. A quick reachability probe (~3 s) skips the mirror pass when the mirror server is down, so a dead mirror never stalls the loop on per-event timeouts; skipped events stay pending in the mirror state and deliver when the mirror returns — **no data loss**.
+- **Isolation invariant (the one rule).** Nothing on the mirror path can delay or fail the primary: its own state file, its own try/except, the reachability guard + bounded timeouts, all exceptions swallowed-and-logged. The primary path stays exactly as reliable as before.
+- **Mirror tab in the Settings dialog** with `Mirror API URL` + `Mirror SFM URL` fields (blank = off). The mirror rides along with the primary — there is no separate enable flag (heartbeat-mirror active iff the primary heartbeat is on *and* `mirror_api_url` is set; event-mirror active iff primary forwarding is on *and* `mirror_sfm_url` is set).
+- New unit tests in `test_event_forwarder.py` covering mirror reachability, the down-mirror skip, separate-state idempotency, and the isolation invariant (a mirror failure leaves the primary's result + state untouched).
+
+### Configuration
+
+New `config.json` keys (all default-empty = off; existing 0.3.x deployments don't change behaviour on auto-update):
+
+| Key | Default | Notes |
+|---|---|---|
+| `mirror_api_url` | `""` | Second heartbeat destination — same URL form as `api_url` (blank = off) |
+| `mirror_sfm_url` | `""` | Second SFM base URL, e.g. `http://10.0.0.x:8200` (blank = off) |
+| `mirror_sfm_state_file` | `""` | Override the mirror's forwarded-sha256 state file. Blank → `<log_dir>\thor_forwarded_mirror.json` |
+
+### Changed
+- Bumped `VERSION` to `0.4.0`
+
+> **Operational note (migration seeding).** To make the mirror re-deliver only the gap since a one-time replica snapshot, copy the primary state file to the mirror state file and drop entries whose `forwarded_at` is after the snapshot. SFM-side dedup covers any overlap. See `docs/mirror-dual-send-design.md`.
+
+
 ## [0.3.1] - 2026-05-20
 
 ### Hot fix

README.md

@@ -1,8 +1,8 @@
 # Thor Watcher
 
-**Version:** 0.3.1
+**Version:** 0.4.1
 
-Micromate (Series 4) watcher agent for Terra-View fleet management. Runs as a Windows system tray application, scans THORDATA for Micromate unit activity, sends heartbeat data to Terra-View, and (optionally) forwards `.IDFH`/`.IDFW` event files to a seismo-relay SFM server.
+Micromate (Series 4) watcher agent for Terra-View fleet management. Runs as a Windows system tray application, scans THORDATA for Micromate unit activity, sends heartbeat data to Terra-View, and (optionally) forwards `.IDFH`/`.IDFW` event files to a seismo-relay SFM server. Heartbeats and events can optionally be **mirrored** to a second server (e.g. a standby/NAS) in addition to the primary.
 
 ---
 
@@ -29,7 +29,7 @@ build.bat
 ```
 
 Produces:
-- `dist\thor-watcher-0.3.1.exe` — upload to Gitea release
+- `dist\thor-watcher-0.4.1.exe` — upload to Gitea release
 - `dist\thor-watcher.exe` — use with Inno Setup
 
 Then run Inno Setup Compiler on `installer.iss` to produce `thor-watcher-setup.exe`.
@@ -71,6 +71,9 @@ Managed through the Settings dialog (right-click tray icon → Settings). A `con
 | `sfm_state_file` | string | `""` | Path to the sha256-keyed state file. Blank → `<log_dir>\thor_forwarded.json` |
 | `sfm_max_forwards_per_pass` | integer | `500` | Cap per pass to drip-feed large backfills |
 | `sfm_max_event_age_days` | integer | `365` | Skip event files older than this many days |
+| `mirror_api_url` | string | `""` | Second heartbeat destination (same URL form as `api_url`). Blank → heartbeat mirror off |
+| `mirror_sfm_url` | string | `""` | Second SFM base URL (e.g. `http://10.0.0.x:8200`). Blank → event mirror off |
+| `mirror_sfm_state_file` | string | `""` | Path to the mirror's sha256 state file. Blank → `<log_dir>\thor_forwarded_mirror.json` |
 
 ---
 
@@ -86,6 +89,21 @@ When `sfm_forward_enabled` is true and `sfm_url` is set, Thor Watcher walks the
 
 ---
 
+## Mirror (Dual-Send)
+
+Thor Watcher can post every heartbeat and event to a **second ("mirror") server** in addition to the primary — useful for keeping a standby box (e.g. the office NAS) as a continuous replica during a server migration, so the eventual cutover is a non-event. **Default off.**
+
+The mirror rides along with the primary — there is no separate enable flag:
+
+- **Heartbeat mirror** is active when the API heartbeat is enabled **and** `mirror_api_url` is set. After the primary heartbeat POST, the same payload is fired at `mirror_api_url`.
+- **Event mirror** is active when SFM forwarding is enabled **and** `mirror_sfm_url` is set. Events are re-forwarded to `mirror_sfm_url` using a **separate** sha256 state file (`mirror_sfm_state_file`, blank → `<log_dir>\thor_forwarded_mirror.json`).
+
+**The mirror can never delay or fail the primary.** The heartbeat mirror is fully wrapped and bounded by the API timeout. The event mirror runs a quick reachability probe (~3 s) first and skips the pass if the mirror server is down — skipped events stay pending in the mirror state and deliver when it returns, so nothing is lost. All mirror exceptions are swallowed-and-logged; the primary path stays exactly as reliable as before.
+
+- **Seeding for a migration.** To re-deliver only the gap since a one-time replica snapshot, copy the primary state file to the mirror state file and drop entries whose `forwarded_at` is after the snapshot. SFM-side dedup covers any overlap. See [`docs/mirror-dual-send-design.md`](docs/mirror-dual-send-design.md).
+
+---
+
 ## Tray Icon Colors
 
 | Color | Meaning |
@@ -121,7 +139,7 @@ Posted to `api_url` on each API interval:
 {
   "source_id": "THOR-PC",
   "source_type": "series4_watcher",
-  "version": "0.3.1",
+  "version": "0.4.1",
   "generated_at": "2026-03-20T14:30:00Z",
   "log_tail": ["...last 25 log lines..."],
   "units": [

config.example.json

@@ -24,5 +24,9 @@
   "sfm_http_timeout": 60,
   "sfm_state_file": "",
   "sfm_max_forwards_per_pass": 500,
-  "sfm_max_event_age_days": 365
+  "sfm_max_event_age_days": 365,
+
+  "mirror_api_url": "",
+  "mirror_sfm_url": "",
+  "mirror_sfm_state_file": ""
 }

docs/mirror-dual-send-design.md

@@ -0,0 +1,51 @@
+# Watcher Mirror (Dual-Send) — Design
+
+**Date:** 2026-06-24 · **Branch:** `feat/mirror-dual-send` (both `thor-watcher` + `series3-watcher`) · **Status:** approved, implementing
+
+## Goal
+Let each watcher post every heartbeat and event to a **second ("mirror") server** in addition to the primary, so the office NAS stays a continuous replica of prod during the migration. The eventual cutover becomes a non-event. **Default off** → existing installs unchanged.
+
+## Pattern
+Classic dual-write migration. The primary path stays **exactly as reliable as today**; the mirror is pure best-effort bonus that can **never delay or fail** the primary.
+
+## The two watchers (parallel changes)
+| | thor-watcher (series4) | series3-watcher (s3) |
+|---|---|---|
+| Config | `config.json` (JSON) | `config.ini` (`[agent]`, INI) |
+| Heartbeat fn | `send_api_payload(payload, api_url, timeout)` | `send_api_payload(payload, api_url)` |
+| Event fn | `event_forwarder.forward_pending(root, sfm_url, state, …)` | same (`event_forwarder` is a sibling port) |
+| Loop | `series4_ingest.run_watcher` | `series3_watcher.run_watcher` |
+| Settings GUI | `thor_settings_dialog.py` | `settings_dialog.py` |
+
+## Design (Approach A — reliable event mirror, best-effort heartbeat)
+
+### Config additions (default empty = off)
+- thor (`config.json`): `mirror_api_url`, `mirror_sfm_url`, `mirror_sfm_state_file` (blank → `<log_dir>/thor_forwarded_mirror.json`).
+- s3 (`config.ini`): `MIRROR_API_URL`, `MIRROR_SFM_URL`, `MIRROR_SFM_STATE_FILE` (blank → `sfm_forwarded_mirror.json`).
+
+The mirror **rides along** with the primary: heartbeat-mirror active iff primary heartbeat on **and** `mirror_api_url` set; event-mirror active iff primary forwarding on **and** `mirror_sfm_url` set. No separate enable flag.
+
+### Heartbeat mirror (best-effort)
+After the primary `send_api_payload`, if `mirror_api_url` is set, fire one more `send_api_payload(payload, mirror_api_url, …)`. Wrapped so it can never raise into the loop; result ignored except a debug log. Bounded by the existing short API timeout (~5 s).
+
+### Event mirror (reliable, isolated)
+- Init a **second** `ForwardState(mirror_state_path)` alongside the primary state.
+- Each forward tick, **after** the primary `forward_pending`, run a second `forward_pending(root, mirror_sfm_url, mirror_state, …)` in its **own** try/except.
+- **Reachability guard:** before the mirror forward, a quick TCP/HTTP probe of `mirror_sfm_url` (~3 s). If unreachable → skip this pass, log, retry next tick. Prevents a down NAS from stalling the loop on per-event timeouts. The mirror state file means skipped events stay pending → delivered when the NAS returns. **No data loss.**
+- Reliable + idempotent via its own sha256 state, fully independent of the primary's state.
+
+### Isolation invariant (the one rule)
+Nothing on the mirror path can delay or fail the primary: separate state file, its own try/except, the reachability guard + bounded timeouts, all exceptions swallowed-and-logged.
+
+### Settings dialog
+Add `Mirror API URL` + `Mirror SFM URL` fields (blank = off) to each watcher's settings dialog.
+
+## Seeding (operational, for this migration)
+The mirror state file should reflect what the NAS already has (everything ≤ the migration snapshot, ~16:23 on 2026-06-24). Recipe: copy the primary state file → mirror state file, then drop entries whose `forwarded_at` is after the snapshot, so the mirror re-delivers exactly the gap. SFM-side dedup covers any overlap. (If a watcher had no events in the gap, a straight copy suffices.)
+
+## Testing
+- thor `test_event_forwarder.py`: mirror uses a separate state file (idempotent, independent); a mirror failure leaves the primary's result + state untouched; reachability guard skips cleanly when the mirror is down.
+- s3: add a minimal test for the same isolation/idempotency.
+
+## Out of scope / handoff
+Rebuilding the Windows installers + redeploying (s3 on the Win7 box, thor on the Win10 box) is the operator's job — this change is **code + tests only**.

event_forwarder.py

@@ -692,6 +692,74 @@ def forward_pending(
     return counts
 
 
+# ── Mirror (dual-send) ────────────────────────────────────────────────────────
+
+
+def mirror_reachable(base_url: str, timeout: float = 3.0) -> bool:
+    """Quick liveness probe of a mirror SFM base URL.
+
+    Run before a mirror forward pass so an unreachable mirror can't stall
+    the watcher loop on a per-event HTTP timeout for every pending file.
+    Probes ``<base>/health`` (the SFM server exposes it).  ANY HTTP
+    response — even 404/500 — means the server is up, so proceed; only a
+    connection-level failure (refused / timed out / DNS) counts as down.
+    Best-effort: never raises.
+    """
+    if not base_url:
+        return False
+    url = base_url.rstrip("/") + "/health"
+    try:
+        with urllib.request.urlopen(
+            urllib.request.Request(url, method="GET"), timeout=timeout
+        ):
+            return True
+    except urllib.error.HTTPError:
+        return True   # got a status back → server is alive
+    except Exception:
+        return False  # refused / timeout / DNS / socket → down
+
+
+def mirror_forward_pass(
+    watch_dir: str,
+    mirror_url: str,
+    mirror_state: ForwardState,
+    *,
+    reachable_fn=mirror_reachable,
+    reachable_timeout: float = 3.0,
+    **forward_kwargs: Any,
+) -> Optional[Dict[str, int]]:
+    """One best-effort forwarding pass against a *mirror* SFM server.
+
+    The dual-send entry point.  Wraps :func:`forward_pending` with two
+    properties that keep the mirror from ever harming the primary path:
+
+    1. **Fast-fail reachability guard** — probe ``mirror_url`` first; if
+       it's down, return ``None`` immediately rather than let
+       :func:`forward_pending` block on a per-event timeout for every
+       pending file.
+    2. **Total exception isolation** — any error (probe, forward, state
+       I/O) is swallowed and reported as ``None``.  This function NEVER
+       raises, so the caller's already-completed primary forward is
+       untouched.
+
+    The mirror keeps its OWN ``ForwardState`` file, so its idempotency
+    and retry are independent of the primary's.  Nothing is lost while
+    the mirror is down — skipped events stay pending and are delivered
+    on a later pass once it returns.
+
+    Returns the :func:`forward_pending` counts dict on a completed pass,
+    or ``None`` if the mirror was unreachable or the pass raised.
+    """
+    try:
+        if not mirror_url:
+            return None
+        if not reachable_fn(mirror_url, reachable_timeout):
+            return None
+        return forward_pending(watch_dir, mirror_url, mirror_state, **forward_kwargs)
+    except Exception:
+        return None
+
+
 # ── Seed-state mode (skip historical backfill on first deploy) ────────────────
 
 

installer.iss

@@ -3,7 +3,7 @@
 
 [Setup]
 AppName=Thor Watcher
-AppVersion=0.3.1
+AppVersion=0.4.1
 AppPublisher=Terra-Mechanics Inc.
 DefaultDirName={pf}\ThorWatcher
 DefaultGroupName=Thor Watcher

series4_ingest.py

@@ -1,5 +1,5 @@
 """
-Thor Watcher — Series 4 Ingest Agent  v0.3.1
+Thor Watcher — Series 4 Ingest Agent  v0.4.1
 
 Micromate (Series 4) ingest agent for Terra-View.
 
@@ -29,7 +29,7 @@ import event_forwarder
 
 # ── Version ───────────────────────────────────────────────────────────────────
 
-VERSION = "0.3.1"
+VERSION = "0.4.1"
 
 
 # ── Config ────────────────────────────────────────────────────────────────────
@@ -69,6 +69,15 @@ def load_config(config_path: str) -> Dict[str, Any]:
         "sfm_state_file":                   "",      # blank → <log_dir>/thor_forwarded.json
         "sfm_max_forwards_per_pass":        500,
         "sfm_max_event_age_days":           365,
+
+        # Mirror (dual-send) — best-effort second destination, default OFF.
+        # See docs/mirror-dual-send-design.md.  Heartbeat-mirror fires iff
+        # api_url AND mirror_api_url are set; event-mirror runs iff SFM
+        # forwarding is on AND mirror_sfm_url is set.  Own state file →
+        # idempotency independent of the primary.
+        "mirror_api_url":         "",
+        "mirror_sfm_url":         "",
+        "mirror_sfm_state_file":  "",   # blank → <log_dir>/thor_forwarded_mirror.json
     }
 
     with open(config_path, "r", encoding="utf-8") as f:
@@ -329,6 +338,12 @@ def run_watcher(state: Dict[str, Any], stop_event: threading.Event) -> None:
     sfm_state_path        = str(cfg.get("sfm_state_file", "")).strip() or \
         os.path.join(state["log_dir"], "thor_forwarded.json")
 
+    # Mirror (dual-send) config
+    MIRROR_API_URL    = str(cfg.get("mirror_api_url", "")).strip()
+    MIRROR_SFM_URL    = str(cfg.get("mirror_sfm_url", "")).strip()
+    mirror_state_path = str(cfg.get("mirror_sfm_state_file", "")).strip() or \
+        os.path.join(state["log_dir"], "thor_forwarded_mirror.json")
+
     log_message(log_file, ENABLE_LOGGING,
         "[cfg] THORDATA_PATH={} SCAN_INTERVAL={}s API_INTERVAL={}s API={} SFM={}".format(
             THORDATA_PATH, SCAN_INTERVAL, API_INTERVAL, bool(API_URL),
@@ -362,6 +377,24 @@ def run_watcher(state: Dict[str, Any], stop_event: threading.Event) -> None:
     else:
         state["sfm_status"] = "disabled"
 
+    # Mirror event-forward state — independent of the primary's.  Created
+    # only when the primary forwarder is on AND a mirror URL is set.
+    mirror_state_obj: Optional[event_forwarder.ForwardState] = None
+    if sfm_state_obj is not None and MIRROR_SFM_URL:
+        try:
+            mirror_state_obj = event_forwarder.ForwardState(mirror_state_path)
+            log_message(log_file, ENABLE_LOGGING,
+                "[mirror] event mirror ready  url={}  state={}  known={}".format(
+                    MIRROR_SFM_URL, mirror_state_path, mirror_state_obj.count()))
+            print("[MIRROR] event mirror ready  url={}".format(MIRROR_SFM_URL))
+        except Exception as exc:
+            log_message(log_file, ENABLE_LOGGING,
+                "[mirror] event mirror init failed: {}".format(exc))
+            mirror_state_obj = None
+    if MIRROR_API_URL:
+        log_message(log_file, ENABLE_LOGGING,
+            "[mirror] heartbeat mirror enabled  url={}".format(MIRROR_API_URL))
+
     state["last_forward"] = None
     state["last_forward_counts"] = None
 
@@ -419,6 +452,13 @@ def run_watcher(state: Dict[str, Any], stop_event: threading.Event) -> None:
                     payload["log_tail"] = _read_log_tail(log_file, 25)
                     response = send_api_payload(payload, API_URL, API_TIMEOUT)
                     last_api_ts = now_ts
+                    # Best-effort heartbeat mirror — never affects primary.
+                    if MIRROR_API_URL:
+                        try:
+                            send_api_payload(payload, MIRROR_API_URL, API_TIMEOUT)
+                        except Exception as exc:
+                            log_message(log_file, ENABLE_LOGGING,
+                                "[mirror] heartbeat post failed: {}".format(exc))
                     if response is not None:
                         state["api_status"] = "ok"
                         if response.get("update_available"):
@@ -459,6 +499,25 @@ def run_watcher(state: Dict[str, Any], stop_event: threading.Event) -> None:
                         print(msg)
                         log_message(log_file, ENABLE_LOGGING, msg)
 
+                    # Best-effort event mirror — own state, fast-fail guard,
+                    # fully isolated.  Runs after the primary each tick.
+                    if mirror_state_obj is not None:
+                        m_counts = event_forwarder.mirror_forward_pass(
+                            THORDATA_PATH, MIRROR_SFM_URL, mirror_state_obj,
+                            max_age_days=SFM_MAX_AGE_DAYS,
+                            quiescence_seconds=SFM_QUIESCENCE,
+                            missing_report_grace_seconds=SFM_GRACE,
+                            timeout=SFM_HTTP_TIMEOUT,
+                            max_per_pass=SFM_MAX_PER_PASS,
+                            logger=lambda m: log_message(log_file, ENABLE_LOGGING, "[mirror] " + m),
+                        )
+                        if m_counts is None:
+                            log_message(log_file, ENABLE_LOGGING,
+                                "[mirror] forward skipped (unreachable/error): {}".format(MIRROR_SFM_URL))
+                        else:
+                            log_message(log_file, ENABLE_LOGGING,
+                                "[mirror] pass forwarded={forwarded} errors={errors}".format(**m_counts))
+
         except Exception as e:
             err = "[loop-error] {}".format(e)
             print(err)

test_event_forwarder.py

@@ -712,5 +712,134 @@ class TestForwardPending(unittest.TestCase):
             self.assertEqual(len(_FakeImportHandler.received), 2)
 
 
+# ── Mirror (dual-send) ───────────────────────────────────────────────────────
+
+
+class TestMirrorReachable(unittest.TestCase):
+
+    def test_empty_url_is_unreachable(self):
+        self.assertFalse(ef.mirror_reachable("", timeout=1.0))
+
+    def test_dead_port_is_unreachable_and_fast(self):
+        # Nothing listens on 127.0.0.1:1 → connection refused → False,
+        # and it must NOT hang (this is the whole point of the guard).
+        t0 = time.time()
+        self.assertFalse(ef.mirror_reachable("http://127.0.0.1:1", timeout=2.0))
+        self.assertLess(time.time() - t0, 2.5)
+
+    def test_any_http_response_counts_as_reachable(self):
+        # The fake server 501s on GET /health, but it's UP — so reachable.
+        server, base = _start_fake_server()
+        try:
+            self.assertTrue(ef.mirror_reachable(base, timeout=2.0))
+        finally:
+            server.shutdown()
+            server.server_close()
+
+
+class TestMirrorForwardPass(unittest.TestCase):
+    """The dual-send entry point: best-effort, isolated, own state."""
+
+    def setUp(self):
+        _FakeImportHandler.received = []
+        self.server, self.base_url = _start_fake_server()
+
+    def tearDown(self):
+        self.server.shutdown()
+        self.server.server_close()
+
+    def _one_event(self, root: Path) -> None:
+        unit = _make_thordata(root, "Project A", "UM11719")
+        _make_event(unit, "UM11719_20231219163444.IDFW", age_seconds=200, content=b"binary")
+        _make_txt(unit, "UM11719_20231219163444.IDFW", age_seconds=100, content=b"report")
+
+    def test_empty_mirror_url_is_noop(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            root = Path(tmp)
+            self._one_event(root)
+            mstate = ef.ForwardState(str(root / "mirror.json"))
+            self.assertIsNone(ef.mirror_forward_pass(str(root), "", mstate, max_age_days=30))
+            self.assertEqual(len(_FakeImportHandler.received), 0)
+
+    def test_skips_when_unreachable_without_posting(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            root = Path(tmp)
+            self._one_event(root)
+            mstate = ef.ForwardState(str(root / "mirror.json"))
+            result = ef.mirror_forward_pass(
+                str(root), self.base_url, mstate,
+                reachable_fn=lambda url, timeout=3.0: False,   # force "down"
+                max_age_days=30, quiescence_seconds=5,
+                missing_report_grace_seconds=60, timeout=5.0,
+            )
+            self.assertIsNone(result)
+            self.assertEqual(mstate.count(), 0)                # nothing forwarded
+            self.assertEqual(len(_FakeImportHandler.received), 0)   # never POSTed
+
+    def test_forwards_when_reachable_using_its_own_state(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            root = Path(tmp)
+            self._one_event(root)
+            mstate = ef.ForwardState(str(root / "mirror.json"))
+            counts = ef.mirror_forward_pass(
+                str(root), self.base_url, mstate,
+                reachable_fn=lambda url, timeout=3.0: True,
+                max_age_days=30, quiescence_seconds=5,
+                missing_report_grace_seconds=60, timeout=5.0,
+            )
+            self.assertIsNotNone(counts)
+            self.assertEqual(counts["forwarded"], 1)
+            self.assertEqual(mstate.count(), 1)
+            self.assertEqual(len(_FakeImportHandler.received), 1)
+
+    def test_never_raises_when_forward_blows_up(self):
+        # Even if forward_pending raises, the mirror swallows it → None.
+        def _boom(*a, **k):
+            raise RuntimeError("boom")
+        with tempfile.TemporaryDirectory() as tmp:
+            root = Path(tmp)
+            self._one_event(root)
+            mstate = ef.ForwardState(str(root / "mirror.json"))
+            orig = ef.forward_pending
+            ef.forward_pending = _boom
+            try:
+                result = ef.mirror_forward_pass(
+                    str(root), self.base_url, mstate,
+                    reachable_fn=lambda url, timeout=3.0: True,
+                    max_age_days=30,
+                )
+            finally:
+                ef.forward_pending = orig
+            self.assertIsNone(result)
+
+    def test_down_mirror_leaves_primary_state_untouched(self):
+        # The invariant: a real down mirror (via the real reachability
+        # probe) is a fast no-op and the primary forward is unaffected.
+        with tempfile.TemporaryDirectory() as tmp:
+            root = Path(tmp)
+            self._one_event(root)
+
+            primary_state = ef.ForwardState(str(root / "primary.json"))
+            pcounts = ef.forward_pending(
+                str(root), self.base_url, primary_state,
+                max_age_days=30, quiescence_seconds=5,
+                missing_report_grace_seconds=60, timeout=5.0,
+            )
+            self.assertEqual(pcounts["forwarded"], 1)
+            primary_snapshot = primary_state.count()
+
+            mstate = ef.ForwardState(str(root / "mirror.json"))
+            t0 = time.time()
+            result = ef.mirror_forward_pass(
+                str(root), "http://127.0.0.1:1", mstate,   # nothing listens
+                max_age_days=30, quiescence_seconds=5,
+                missing_report_grace_seconds=60, timeout=5.0,
+            )
+            self.assertIsNone(result)
+            self.assertLess(time.time() - t0, 3.5)          # fast-failed, didn't hang
+            self.assertEqual(mstate.count(), 0)
+            self.assertEqual(primary_state.count(), primary_snapshot)   # untouched
+
+
 if __name__ == "__main__":
     unittest.main()

test_thor_tray.py

@@ -0,0 +1,81 @@
+"""
+Tests for thor_tray's thread lifecycle.
+
+Regression guard for the bug where saving settings — which restarts the
+watcher thread via ``_restart_watcher`` — also killed the auto-updater
+thread, because both shared a single ``stop_event``. The updater must key
+off a separate lifetime event (``_app_stop``) that a watcher restart never
+disturbs; it should only stop when the app actually exits.
+"""
+import sys
+import time
+import threading
+import unittest
+from unittest import mock
+
+# Thor's tray pulls in Windows-only GUI deps at import time; stub them so the
+# module imports on a headless dev/CI box.
+for _name in ("pystray", "PIL", "PIL.Image", "PIL.ImageDraw"):
+    sys.modules.setdefault(_name, mock.MagicMock())
+
+import thor_tray  # noqa: E402
+
+
+class TrayThreadLifecycle(unittest.TestCase):
+    def setUp(self):
+        # Keep _start_watcher cheap: a no-op watcher loop so restarting the
+        # watcher doesn't spin up the real THORDATA scanner / network heartbeat.
+        patcher = mock.patch.object(
+            thor_tray.watcher, "run_watcher", lambda state, stop_event: None
+        )
+        patcher.start()
+        self.addCleanup(patcher.stop)
+
+    def test_app_stop_is_separate_lifetime_event(self):
+        app = thor_tray.WatcherTray()
+        self.assertIsInstance(app._app_stop, threading.Event)
+        self.assertIsNot(app._app_stop, app.stop_event)
+        self.assertFalse(app._app_stop.is_set())
+
+    def test_exit_signals_app_stop(self):
+        app = thor_tray.WatcherTray()
+        icon = mock.MagicMock()
+        app._exit(icon, None)
+        self.assertTrue(app._app_stop.is_set())
+        icon.stop.assert_called_once()
+
+    def test_restart_watcher_leaves_watcher_stop_unset(self):
+        app = thor_tray.WatcherTray()
+        app._restart_watcher()
+        self.assertFalse(app.stop_event.is_set())
+
+    def test_updater_survives_watcher_restart_then_stops_on_exit(self):
+        app = thor_tray.WatcherTray()
+        app._icon = None
+        with mock.patch.object(thor_tray, "check_for_update", return_value=(None, None)), \
+                mock.patch.object(thor_tray, "_update_log"), \
+                mock.patch.object(app, "_tray_status", return_value="ok"):
+            t = threading.Thread(
+                target=app._icon_updater, daemon=True, name="test-updater"
+            )
+            t.start()
+            time.sleep(0.1)
+            self.assertTrue(t.is_alive(), "updater failed to start")
+
+            # A settings save restarts the watcher — it must NOT kill the updater.
+            app._restart_watcher()
+            time.sleep(0.2)
+            self.assertTrue(
+                t.is_alive(), "updater thread died on watcher restart (the bug)"
+            )
+
+            # Real app exit DOES stop the updater.
+            app._app_stop.set()
+            t.join(timeout=2)
+            self.assertFalse(
+                t.is_alive(), "updater thread did not stop on app exit"
+            )
+
+
+if __name__ == "__main__":
+    unittest.main()

thor_settings_dialog.py

@@ -1,5 +1,5 @@
 """
-Thor Watcher — Settings Dialog  v0.3.1
+Thor Watcher — Settings Dialog  v0.4.1
 
 Provides a Tkinter settings dialog that doubles as a first-run wizard.
 
@@ -47,6 +47,11 @@ DEFAULTS = {
     "sfm_state_file":                   "",
     "sfm_max_forwards_per_pass":        500,
     "sfm_max_event_age_days":           365,
+
+    # Mirror (dual-send) — best-effort second destination, default OFF.
+    "mirror_api_url":         "",
+    "mirror_sfm_url":         "",
+    "mirror_sfm_state_file":  "",
 }
 
 
@@ -220,6 +225,14 @@ class SettingsDialog:
         self.var_sfm_max_age_days       = tk.StringVar(value=str(v.get("sfm_max_event_age_days", 365)))
         self.var_sfm_state_file         = tk.StringVar(value=str(v.get("sfm_state_file", "")))
 
+        # Mirror (dual-send) — best-effort second destination
+        raw_mirror = str(v.get("mirror_api_url", ""))
+        if raw_mirror.endswith(_suffix):
+            raw_mirror = raw_mirror[:-len(_suffix)]
+        self.var_mirror_api_url        = tk.StringVar(value=raw_mirror)
+        self.var_mirror_sfm_url        = tk.StringVar(value=str(v.get("mirror_sfm_url", "")))
+        self.var_mirror_sfm_state_file = tk.StringVar(value=str(v.get("mirror_sfm_state_file", "")))
+
     # ── UI construction ───────────────────────────────────────────────────────
 
     def _build_ui(self):
@@ -245,6 +258,7 @@ class SettingsDialog:
         self._build_tab_scanning(nb)
         self._build_tab_logging(nb)
         self._build_tab_forwarding(nb)
+        self._build_tab_mirror(nb)
         self._build_tab_updates(nb)
 
         btn_frame = tk.Frame(outer)
@@ -484,6 +498,49 @@ class SettingsDialog:
         finally:
             self._sfm_test_btn.config(state="normal")
 
+    def _build_tab_mirror(self, nb):
+        f = self._tab_frame(nb, "Mirror")
+
+        intro = (
+            "Optional dual-send: post each heartbeat and event to a SECOND\n"
+            "(\"mirror\") server in addition to the primary. Best-effort — the\n"
+            "mirror can never delay or fail the primary. Leave blank to disable."
+        )
+        tk.Label(f, text=intro, justify="left", fg="#1a5276", wraplength=420).grid(
+            row=0, column=0, columnspan=2, sticky="w", padx=(8, 8), pady=(6, 8)
+        )
+
+        _add_label_entry(f, 1, "Mirror Terra-View URL", self.var_mirror_api_url)
+        _add_label_entry(f, 2, "Mirror SFM URL", self.var_mirror_sfm_url)
+
+        def browse_mirror_state():
+            p = filedialog.asksaveasfilename(
+                title="Select Mirror State File",
+                defaultextension=".json",
+                filetypes=[("JSON files", "*.json"), ("All files", "*.*")],
+                initialfile=os.path.basename(
+                    self.var_mirror_sfm_state_file.get() or "thor_forwarded_mirror.json"),
+                initialdir=os.path.dirname(self.var_mirror_sfm_state_file.get() or "C:\\"),
+            )
+            if p:
+                self.var_mirror_sfm_state_file.set(p.replace("/", "\\"))
+
+        _add_label_browse_entry(f, 3, "Mirror State File", self.var_mirror_sfm_state_file,
+                                browse_mirror_state)
+
+        help_text = (
+            "Mirror Terra-View URL → base like http://10.0.0.x:8001 (heartbeats).\n"
+            "Mirror SFM URL → base like http://10.0.0.x:8200 (events).\n"
+            "The event mirror keeps its OWN state file, so nothing is lost while\n"
+            "the mirror is down — pending events are delivered once it returns.\n"
+            "A quick reachability check skips the mirror cleanly when unreachable,\n"
+            "so the primary is never slowed.\n"
+            "State file blank → defaults to <log_dir>\\thor_forwarded_mirror.json."
+        )
+        tk.Label(f, text=help_text, justify="left", fg="#555555", wraplength=420).grid(
+            row=4, column=0, columnspan=2, sticky="w", padx=(8, 8), pady=(8, 4)
+        )
+
     def _build_tab_updates(self, nb):
         f = self._tab_frame(nb, "Updates")
 
@@ -599,6 +656,12 @@ class SettingsDialog:
             sfm_url = ""
         sfm_url = sfm_url.rstrip("/")  # event_forwarder adds the endpoint path
 
+        # Mirror (dual-send) — best-effort second destination.
+        mirror_api_url = self.var_mirror_api_url.get().strip()
+        if mirror_api_url:
+            mirror_api_url = mirror_api_url.rstrip("/") + "/api/series4/heartbeat"
+        mirror_sfm_url = self.var_mirror_sfm_url.get().strip().rstrip("/")
+
         values = {
             "thordata_path":      self.var_thordata_path.get().strip(),
             "scan_interval":      int_values["Scan Interval"],
@@ -623,6 +686,10 @@ class SettingsDialog:
             "sfm_max_forwards_per_pass":        int_values["Max Forwards Per Pass"],
             "sfm_max_event_age_days":           int_values["Max Event Age (days)"],
             "sfm_state_file":                   self.var_sfm_state_file.get().strip(),
+
+            "mirror_api_url":        mirror_api_url,
+            "mirror_sfm_url":         mirror_sfm_url,
+            "mirror_sfm_state_file":  self.var_mirror_sfm_state_file.get().strip(),
         }
 
         try:

thor_tray.py

@@ -1,5 +1,5 @@
 """
-Thor Watcher — System Tray Launcher  v0.3.1
+Thor Watcher — System Tray Launcher  v0.4.1
 Requires: pystray, Pillow, tkinter (stdlib)
 
 Run with:  pythonw thor_tray.py   (no console window)
@@ -334,7 +334,8 @@ def _show_cancel_message():
 class WatcherTray:
     def __init__(self):
         self.state = {}
-        self.stop_event = threading.Event()
+        self.stop_event = threading.Event()   # watcher lifecycle; replaced on restart
+        self._app_stop = threading.Event()    # app lifetime; only set on exit/update
         self._watcher_thread = None
         self._icon = None
         self._menu_lock = threading.Lock()
@@ -390,6 +391,7 @@ class WatcherTray:
                 subprocess.Popen(["explorer", HERE])
 
     def _exit(self, icon, item):
+        self._app_stop.set()
         self.stop_event.set()
         icon.stop()
 
@@ -478,7 +480,7 @@ class WatcherTray:
         # line in the log soon after startup; subsequent checks every ~5 min.
         update_check_counter = 27
 
-        while not self.stop_event.is_set():
+        while not self._app_stop.is_set():
             icon_status = self._tray_status()
 
             if self._icon is not None:
@@ -504,7 +506,7 @@ class WatcherTray:
                     self._do_update(url)
                     return
 
-            self.stop_event.wait(timeout=10)
+            self._app_stop.wait(timeout=10)
 
     def _do_update(self, download_url=None):
         """Notify tray then apply update. If url is None, fetch it first."""
@@ -519,6 +521,7 @@ class WatcherTray:
 
         success = apply_update(download_url)
         if success:
+            self._app_stop.set()
             self.stop_event.set()
             if self._icon is not None:
                 self._icon.stop()