diff --git a/findings.md b/findings.md
new file mode 100644
index 00000000..e916f1cb
--- /dev/null
+++ b/findings.md
@@ -0,0 +1,97 @@
+# Findings — Bugs & Improvements (Non-Critical)
+
+## Bugs
+
+### 🟠 High
+
+| # | File | Line | Issue | Suggested Fix |
+|---|------|------|-------|---------------|
+| 1 | `mechanism_classifier.ex` | 314-317 | `get_lat`/`get_lon` crash on nil — `nil / 1.0` raises `ArithmeticError` if radar lookup returns nil coords | Add pattern match for nil or guard before division |
+| 2 | `path_compute.ex` | 433 | `conditions.abs_humidity` nil crash — `nil * dist_km` raises if conditions map is missing `:abs_humidity` | Use `Map.get(conditions, :abs_humidity, 7.5)` with fallback |
+| 3 | `beacon_live/index.ex` | 119 | `path_with_prefix` creates `//beacons` URLs — `"/" <> path` doubles slash on already-prefixed paths | `String.trim_leading(path, "/")` |
+| 4 | `map_live.ex` | 1053 | `flash_group` called outside `layouts.ex` — violates AGENTS.md rule | Include equivalent in-line FlashGroup component or restructure to use `Layouts.app` |
+| 5 | `config/runtime.exs` | 142, 386 | `EMAIL_SERVER` not validated — unset produces empty SNI causing silent TLS handshake failure | Raise at boot when required env vars are missing (like `DATABASE_URL` does) |
+| 6 | `notify_listener.ex` | 119-126 | `Task.start/1` linked to caller — crash in task kills the GenServer, contradicting moduledoc | Use `Task.Supervisor.start_child` or wrap body in `try/rescue` |
+| 7 | `notify_listener.ex` | 36, 40-51 | No `Process.monitor` on `Postgrex.Notifications` — if PG notify connection crashes, GenServer never learns | Add `Process.monitor` and handle `{:DOWN, ...}` in `handle_info` |
+
+### 🟡 Medium
+
+| # | File | Line | Issue | Suggested Fix |
+|---|------|------|-------|---------------|
+| 8 | `radio.ex` | 128, 157 | N+1 queries — `list_contacts_for_user` and `list_contacts_involving_callsign` don't preload `:user` | Add `|> Repo.preload(:user)` before `Repo.all()` |
+| 9 | `radio.ex` | 751-757 | Missing indexes — dedup query filters on `band`, `qso_timestamp`, `flagged_invalid` with no covering index | Add partial index on `(band, qso_timestamp) WHERE flagged_invalid = false` |
+| 10 | `grid.ex` | 31-36 | `conus_points/0` recomputes ~94k elements on every call — pure function, never memoized | Memoize with module attribute `@conus_points conus_points()` |
+| 11 | `endpoint.ex` | 7-12 | Session cookie is signed but not encrypted — payload is readable though tamper-proof | Add `encryption_salt` to `@session_options` |
+| 12 | `accounts.ex` | 528-538 | Fetches all tokens before deleting them — two queries where one suffices | Use `Repo.delete_all(from t in UserToken, where: t.user_id == ^user.id)` |
+| 13 | `profiles_file.ex` | 169-177 | Unhandled `:zlib.gunzip/1` exception — corrupt gzip files raise through cache wrapper | Wrap in `try/rescue` |
+| 14 | `scores_file.ex` | 515 | Direct ETS `match_delete` bypassing Cache API | Use `Cache.invalidate` or `Cache` public API |
+| 15 | `profiles_file.ex` | 323 | Same direct ETS access as above | Same fix |
+| 16 | `path_compute.ex` | 381-394 | Six redundant list traversals — 12 passes over 9 profiles for what could be 1 `Enum.reduce` | Single pass with `Enum.reduce` |
+| 17 | `hf_muf.ex` | 51 | `sec_i_factor(@ref_distance_km)` recomputed on every call — constant input | Precompute with module attribute |
+| 18 | `config/config.exs` | 163 | `EXLA.Backend` configured for all envs but `nx`/`exla` are dev/test-only deps | Guard with `if Mix.env() in [:dev, :test]` |
+
+### 🟢 Low
+
+| # | File | Line | Issue | Suggested Fix |
+|---|------|------|-------|---------------|
+| 19 | `router.ex` | 165 | Login rate limit 30/min per IP may be generous for brute-force | Consider lowering to 10-15/min |
+| 20 | `application.ex` | 107-109 | Dev/test model loading blocks supervisor start | Wrap in `Task.start` |
+| 21 | `scorer.ex` | 126-138 | `classify_time_period` guard boundaries have gap at exactly `-3.0` | Switch to `cond` with inclusive/exclusive clarity |
+| 22 | `scorer.ex` | 636 | `||` for default when `//` is more intention-revealing | Replace `contact.pos1["lon"] \|\| -97.0` with `//` |
+| 23 | `path_compute.ex` | 356-357 | Eager `Repo.get(Station, ...)` instead of preloading assoc | Preload `:station` upstream |
+| 24 | `radio.ex` | 1203 | Hardcoded cache key `{ContactMapController, :gzipped_payload}` fragile to module rename | Extract to a named key in `ContactMapController` |
+| 25 | `user.ex` | — | Missing `has_many :contacts` and `has_many :beacons` associations | Add for convenience (not a bug, test callers use raw queries) |
+| 26 | `radio.ex` | 337 | Missing partial indexes for enrichment queries | Create filtered indexes on `(qso_timestamp) WHERE weather_status IN ('pending','failed')` |
+
+---
+
+## Improvements
+
+### Architecture & Design
+
+| # | Area | Suggestion |
+|---|------|------------|
+| 1 | `contact_live_test.exs` (3505 lines) | Split into smaller files — currently 2.5x next largest file, uses `async: true` with shared state, relies on `send(lv.pid, ...)` / `:sys.get_state` |
+| 2 | **18 `Process.sleep` usages** in tests | Replace with `Process.monitor` + `assert_receive` or `:sys.get_state` per AGENTS.md |
+| 3 | **25 `Process.alive?` assertions** in tests | Assert on DOM output instead — only verifies process didn't crash, not that handler did anything |
+| 4 | `route.ex` | `get "/"` page controller serves HTML _and_ markdown via `serve_markdown_if_requested` — bypasses secure headers on markdown path |
+| 5 | `router.ex` | Some public routes (`/docs/api/openapi.yaml`) are inside `:browser` pipeline but outside `live_session` — comment explains it's intentional but fragile |
+
+### Test Coverage Gaps
+
+| Module | Status |
+|--------|--------|
+| `lib/microwaveprop/ionosphere.ex` | **Untested** |
+| `lib/microwaveprop/mailer.ex` | **Untested** |
+| `lib/microwaveprop/repo.ex` | **Untested** |
+| `lib/microwaveprop/space_weather.ex` | **Untested** |
+| `about_live.ex` | Real DB query logic, **untested** |
+
+### Config & Tooling
+
+| # | Finding | Suggested Fix |
+|---|---------|---------------|
+| 1 | `LIVE_VIEW_SIGNING_SALT` hardcoded in `config.exs`, not read from env | Read from `System.get_env` in `runtime.exs` |
+| 2 | `:precommit` uses `deps.unlock --unused` (modifies lockfile) | Use `--check-unused` for read-only check |
+| 3 | `Credo.Check.Warning.UnsafeToAtom` disabled | Re-enable to catch `String.to_atom(user_input)` DOS vector |
+| 4 | `Credo.Check.Readability.Specs` disabled | Consider re-enabling for production codebase |
+| 5 | `Credo.Check.Warning.LeakyEnvironment` disabled | Re-enable to catch accidental env var logging |
+
+### Performance Hotspots
+
+| # | Area | Impact |
+|---|------|--------|
+| 1 | `grid.ex:31` — `conus_points()` rebuilds ~94k items per call | **Highest impact fix** — memoize with `@conus_points` |
+| 2 | `radio.ex` dedup queries — missing indexes | Growing table, will degrade over time |
+| 3 | Enrichment queries — missing partial indexes | Each `contacts_needing_enrichment` call scans entire table |
+| 4 | `path_compute.ex:381-394` — 12 list traversals for 9-element profile lists | Small today, but unnecessary overhead in hot path |
+
+### Security (Remaining)
+
+| # | Finding | Severity |
+|---|---------|----------|
+| 1 | Session cookie missing encryption salt (endpoint.ex:7-12) | Medium |
+| 2 | `String.to_atom/1` not warned by Credo (`.credo.exs` has `UnsafeToAtom` disabled) | Low |
+| 3 | Login rate limit at 30/min may be generous | Low |
+| 4 | `build_contact_changes` in `radio.ex:1277` uses `String.to_existing_atom(key)` — safe due to whitelist, but fragile | Low |
+| 5 | Markdown path bypasses secure browser headers | Low (mitigated by plain-text content type) |
diff --git a/lib/microwaveprop/application.ex b/lib/microwaveprop/application.ex
index 0828f498..14d8f879 100644
--- a/lib/microwaveprop/application.ex
+++ b/lib/microwaveprop/application.ex
@@ -75,8 +75,24 @@ defmodule Microwaveprop.Application do
     # the Oban supervisor starts (above in `children`).
     :ok = Microwaveprop.ObanErrorReporter.attach()
 
-    # Run migrations after Repo is started
-    _ = Microwaveprop.Release.migrate()
+    # Run migrations after Repo is started. Wrapped in a background
+    # Task so the application supervisor doesn't block on long-running
+    # migrations on pod boot. Errors are logged but don't crash boot —
+    # the health check will catch schema mismatches.
+    Task.start(fn ->
+      try do
+        case Microwaveprop.Release.migrate() do
+          results when is_list(results) ->
+            Logger.info("Database migrations completed (#{length(results)} repos)")
+
+          other ->
+            Logger.warning("Database migrations returned: #{inspect(other)}")
+        end
+      rescue
+        e ->
+          Logger.error("Database migrations failed: #{Exception.format(:error, e, __STACKTRACE__)}")
+      end
+    end)
 
     # Warm GridCache from the latest persisted ProfilesFile so /weather
     # has data immediately after a pod restart. Runs after the GridCache
diff --git a/lib/microwaveprop/radio.ex b/lib/microwaveprop/radio.ex
index 0fecd8b9..26664f50 100644
--- a/lib/microwaveprop/radio.ex
+++ b/lib/microwaveprop/radio.ex
@@ -732,6 +732,15 @@ defmodule Microwaveprop.Radio do
         changeset = Ecto.Changeset.add_error(changeset, :grid1, "could not resolve grid to coordinates")
         {:error, %{changeset | action: :insert}}
     end
+  rescue
+    e in Ecto.ConstraintError ->
+      # Unique constraint violation from a concurrent insert — the
+      # dedup check at `insert_validated_contact` raced with another
+      # process. Re-check and return the existing contact.
+      case find_duplicate_contact(changeset) do
+        nil -> {:error, :constraint_error}
+        existing -> {:error, :duplicate, existing}
+      end
   end
 
   defp find_duplicate_contact(changeset) do
diff --git a/lib/microwaveprop/radio/contact.ex b/lib/microwaveprop/radio/contact.ex
index 3768aa60..d5cf0b24 100644
--- a/lib/microwaveprop/radio/contact.ex
+++ b/lib/microwaveprop/radio/contact.ex
@@ -82,7 +82,7 @@ defmodule Microwaveprop.Radio.Contact do
   @type t :: %__MODULE__{}
 
   @required_fields ~w(station1 station2 qso_timestamp band)a
-  @optional_fields ~w(grid1 grid2 pos1 pos2 distance_km user_id mode user_declared_prop_mode height1_ft height2_ft private notes)a
+  @optional_fields ~w(grid1 grid2 pos1 pos2 distance_km mode user_declared_prop_mode height1_ft height2_ft private notes)a
 
   @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(contact, attrs) do
diff --git a/lib/microwaveprop_web/api/rate_limiter.ex b/lib/microwaveprop_web/api/rate_limiter.ex
index 8594e638..c8bdb750 100644
--- a/lib/microwaveprop_web/api/rate_limiter.ex
+++ b/lib/microwaveprop_web/api/rate_limiter.ex
@@ -101,7 +101,7 @@ defmodule MicrowavepropWeb.Api.RateLimiter do
 
   defp bucket_for(conn, opts) do
     case conn.assigns[:current_api_token] do
-      %{id: id} when is_binary(id) ->
+      %{id: id} when not is_nil(id) ->
         {{:token, id}, Keyword.get(opts, :auth_limit, @default_auth_limit)}
 
       _ ->
diff --git a/lib/microwaveprop_web/live/path_live.ex b/lib/microwaveprop_web/live/path_live.ex
index 99cdfb4d..bab9e49d 100644
--- a/lib/microwaveprop_web/live/path_live.ex
+++ b/lib/microwaveprop_web/live/path_live.ex
@@ -107,9 +107,22 @@ defmodule MicrowavepropWeb.PathLive do
 
     is_gps = p["source"] == "gps"
 
+    # Clear stale results when URL params change — otherwise a cached
+    # result from a previous calculation persists when the user navigates
+    # to a different source/destination/band combination.
+    new_source = if(is_gps, do: socket.assigns.source, else: p["source"])
+    params_changed? = params_differ?(socket, p, new_source)
+
+    socket =
+      if params_changed? do
+        assign(socket, result: nil, error: nil)
+      else
+        socket
+      end
+
     socket =
       assign(socket,
-        source: if(is_gps, do: socket.assigns.source, else: p["source"]),
+        source: new_source,
         destination: p["destination"],
         band: p["band"],
         src_height_ft: p["src_height_ft"],
@@ -133,6 +146,18 @@ defmodule MicrowavepropWeb.PathLive do
     end
   end
 
+  defp params_differ?(socket, p, new_source) do
+    socket.assigns.result != nil and
+      (new_source != socket.assigns.source or
+         p["destination"] != socket.assigns.destination or
+         p["band"] != socket.assigns.band or
+         p["src_height_ft"] != socket.assigns.src_height_ft or
+         p["dst_height_ft"] != socket.assigns.dst_height_ft or
+         p["tx_power_dbm"] != socket.assigns.tx_power_dbm or
+         p["src_gain_dbi"] != socket.assigns.src_gain_dbi or
+         p["dst_gain_dbi"] != socket.assigns.dst_gain_dbi)
+  end
+
   # Loads a cached rover-planning Path and rebuilds the @result map
   # PathLive's render expects. The blob lives under `result["term"]`
   # (Base64-encoded `:erlang.term_to_binary/1` of PathCompute's full
diff --git a/priv/repo/migrations/20260529201755_add_contacts_dedup_index.exs b/priv/repo/migrations/20260529201755_add_contacts_dedup_index.exs
new file mode 100644
index 00000000..8f49adbb
--- /dev/null
+++ b/priv/repo/migrations/20260529201755_add_contacts_dedup_index.exs
@@ -0,0 +1,44 @@
+defmodule Microwaveprop.Repo.Migrations.AddContactsDedupIndex do
+  use Ecto.Migration
+
+  def up do
+    # Remove existing duplicates before creating the unique index.
+    # Within each group of (band, qso_timestamp, normalized station pair,
+    # normalized grid pair), keep only the first-inserted contact and
+    # remove later duplicates. Flagged-invalid contacts are excluded
+    # from the index predicate, so they never cause violations.
+    execute """
+    DELETE FROM contacts
+    WHERE id IN (
+      SELECT id FROM (
+        SELECT id,
+               ROW_NUMBER() OVER (
+                 PARTITION BY band, qso_timestamp,
+                   LEAST(upper(station1), upper(station2)),
+                   GREATEST(upper(station1), upper(station2)),
+                   LEAST(upper(grid1), upper(grid2)),
+                   GREATEST(upper(grid1), upper(grid2))
+                 ORDER BY inserted_at, id
+               ) AS rn
+        FROM contacts
+        WHERE flagged_invalid = false
+      ) dup
+      WHERE dup.rn > 1
+    )
+    """
+
+    execute """
+    CREATE UNIQUE INDEX contacts_dedup_idx ON contacts
+      (band, qso_timestamp,
+       LEAST(upper(station1), upper(station2)),
+       GREATEST(upper(station1), upper(station2)),
+       LEAST(upper(grid1), upper(grid2)),
+       GREATEST(upper(grid1), upper(grid2)))
+      WHERE flagged_invalid = false
+    """
+  end
+
+  def down do
+    execute "DROP INDEX contacts_dedup_idx"
+  end
+end
diff --git a/test/microwaveprop/radio/contact_edit_test.exs b/test/microwaveprop/radio/contact_edit_test.exs
index 629e56ba..7f2a42d2 100644
--- a/test/microwaveprop/radio/contact_edit_test.exs
+++ b/test/microwaveprop/radio/contact_edit_test.exs
@@ -331,8 +331,8 @@ defmodule Microwaveprop.Radio.ContactEditTest do
 
     defp owned_contact(user) do
       {:ok, contact} =
-        %Contact{}
-        |> Contact.changeset(Map.put(@contact_attrs, :user_id, user.id))
+        %Contact{user_id: user.id}
+        |> Contact.changeset(@contact_attrs)
         |> Microwaveprop.Repo.insert()
 
       contact
@@ -543,8 +543,8 @@ defmodule Microwaveprop.Radio.ContactEditTest do
 
     test "true when contact.user_id matches the user", %{user: user} do
       {:ok, contact} =
-        %Contact{}
-        |> Contact.changeset(Map.put(@contact_attrs, :user_id, user.id))
+        %Contact{user_id: user.id}
+        |> Contact.changeset(@contact_attrs)
         |> Microwaveprop.Repo.insert()
 
       assert Radio.owner?(contact, user)
diff --git a/test/microwaveprop/radio_test.exs b/test/microwaveprop/radio_test.exs
index f56986f6..2004f574 100644
--- a/test/microwaveprop/radio_test.exs
+++ b/test/microwaveprop/radio_test.exs
@@ -21,9 +21,12 @@ defmodule Microwaveprop.RadioTest do
       distance_km: Decimal.new("295")
     }
 
+    merged = Map.merge(default, attrs)
+    {user_id, changeset_attrs} = Map.pop(merged, :user_id)
+
     {:ok, contact} =
-      %Contact{}
-      |> Contact.changeset(Map.merge(default, attrs))
+      %Contact{user_id: user_id}
+      |> Contact.changeset(changeset_attrs)
       |> Repo.insert()
 
     contact
diff --git a/test/microwaveprop_web/live/contact_live_test.exs b/test/microwaveprop_web/live/contact_live_test.exs
index f4d9e7eb..af776b7e 100644
--- a/test/microwaveprop_web/live/contact_live_test.exs
+++ b/test/microwaveprop_web/live/contact_live_test.exs
@@ -39,12 +39,12 @@ defmodule MicrowavepropWeb.ContactLiveTest do
       distance_km: Decimal.new("295")
     }
 
-    {changeset_attrs, direct_attrs} = Map.split(Map.merge(default, attrs), [:user_submitted])
+    merged = Map.merge(default, attrs)
+    {user_id, changeset_attrs} = Map.pop(merged, :user_id)
 
     {:ok, contact} =
-      %Contact{}
-      |> Contact.changeset(direct_attrs)
-      |> Ecto.Changeset.change(changeset_attrs)
+      %Contact{user_id: user_id}
+      |> Contact.changeset(changeset_attrs)
       |> Repo.insert()
 
     contact
diff --git a/test/microwaveprop_web/live/user_profile_live_test.exs b/test/microwaveprop_web/live/user_profile_live_test.exs
index 6673fa9d..d2db90d8 100644
--- a/test/microwaveprop_web/live/user_profile_live_test.exs
+++ b/test/microwaveprop_web/live/user_profile_live_test.exs
@@ -26,9 +26,12 @@ defmodule MicrowavepropWeb.UserProfileLiveTest do
       user_id: user.id
     }
 
+    merged = Map.merge(defaults, attrs)
+    {user_id, changeset_attrs} = Map.pop(merged, :user_id)
+
     {:ok, contact} =
-      %Contact{}
-      |> Contact.changeset(Map.merge(defaults, attrs))
+      %Contact{user_id: user_id}
+      |> Contact.changeset(changeset_attrs)
       |> Repo.insert()
 
     contact