diff --git a/doc/preview.txt b/doc/preview.txt
index ed3c13e..f16b1ae 100644
--- a/doc/preview.txt
+++ b/doc/preview.txt
@@ -183,8 +183,8 @@ override individual fields by passing a table instead: >lua
   `latex`              latexmk -pdf → PDF (with clean support)
   `pdflatex`           pdflatex → PDF (single pass, no latexmk)
   `tectonic`           tectonic → PDF (Rust-based LaTeX engine)
-  `markdown`           pandoc → HTML (standalone, embedded)
-  `github`             pandoc → HTML (GitHub-styled, `-f gfm` input)
+  `markdown`           pandoc → HTML (standalone, KaTeX math)
+  `github`             pandoc → HTML (GitHub-styled, `-f gfm`, KaTeX math)
   `asciidoctor`        asciidoctor → HTML (AsciiDoc with SSE reload)
   `plantuml`           plantuml → SVG (UML diagrams, `.puml`)
   `mermaid`            mmdc → SVG (Mermaid diagrams, `.mmd`)
@@ -193,34 +193,36 @@ override individual fields by passing a table instead: >lua
 Math rendering (pandoc presets): ~
                                                         *preview-math*
 
-The `markdown` and `github` presets use `--mathml` by default, which converts
-TeX math to native MathML markup rendered by the browser. This is the only
-math option compatible with `--embed-resources` (self-contained HTML).
+The `markdown` and `github` presets use `--katex` by default, which inserts a
+`<script>` tag that loads KaTeX from a CDN at view time. The browser fetches
+the assets once and caches them, so math renders instantly on subsequent loads.
+Requires internet on first view.
 
-`--mathjax` and `--katex` insert `<script>` tags that load JavaScript and
-fonts from a CDN at runtime. Pandoc's `--embed-resources` cannot inline these
-dynamic dependencies, so math fails to render in the output.
-
-To use KaTeX or MathJax instead, override `args` to drop `--embed-resources`
-(the output will require internet access). For example, to work with
-github-flavored markdown (gfm): >lua
+For offline use, swap in `--mathml` via `extra_args`. MathML is rendered
+natively by the browser with no external dependencies: >lua
 
     vim.g.preview = {
-      github = {
-        args = function(ctx)
-          return {
-            '-f',
-            'gfm',
-            ctx.file,
-            '-s',
-            '--katex',
-            '--css',
-            'https://cdn.jsdelivr.net/gh/pixelbrackets/gfm-stylesheet@master/dist/gfm.css',
-            '-o',
-            ctx.output,
-          }
-        end,
-      },
+      github = { extra_args = { '--mathml' } },
+    }
+<
+
+Note: pandoc's math flags (`--katex`, `--mathml`, `--mathjax`) are mutually
+exclusive — last flag wins. Adding `--mathml` via `extra_args` (which is
+appended after `args`) overrides `--katex`.
+
+Self-contained output with `--embed-resources`: >lua
+
+    vim.g.preview = {
+      github = { extra_args = { '--embed-resources' } },
+    }
+<
+
+This inlines all external resources into the HTML. With `--katex` this adds
+~15s of compile time per save (pandoc fetches KaTeX from the CDN during
+compilation). Pair with `--mathml` to avoid the penalty: >lua
+
+    vim.g.preview = {
+      github = { extra_args = { '--embed-resources', '--mathml' } },
     }
 <
 
diff --git a/lua/preview/compiler.lua b/lua/preview/compiler.lua
index 5480d57..90f7367 100644
--- a/lua/preview/compiler.lua
+++ b/lua/preview/compiler.lua
@@ -12,6 +12,8 @@ local log = require('preview.log')
 ---@field viewer? table
 ---@field viewer_open? boolean
 ---@field open_watcher? uv.uv_fs_event_t
+---@field output_watcher? uv.uv_fs_event_t
+---@field has_errors? boolean
 ---@field debounce? uv.uv_timer_t
 ---@field bwp_autocmd? integer
 ---@field unload_autocmd? integer
@@ -41,6 +43,17 @@ local function stop_open_watcher(bufnr)
   s.open_watcher = nil
 end
 
+---@param bufnr integer
+local function stop_output_watcher(bufnr)
+  local s = state[bufnr]
+  if not (s and s.output_watcher) then
+    return
+  end
+  s.output_watcher:stop()
+  s.output_watcher:close()
+  s.output_watcher = nil
+end
+
 ---@param bufnr integer
 local function close_viewer(bufnr)
   local s = state[bufnr]
@@ -56,16 +69,17 @@ end
 ---@param provider preview.ProviderConfig
 ---@param ctx preview.Context
 ---@param output string
+---@return integer
 local function handle_errors(bufnr, name, provider, ctx, output)
   local errors_mode = provider.errors
   if errors_mode == nil then
     errors_mode = 'diagnostic'
   end
   if not (provider.error_parser and errors_mode) then
-    return
+    return 0
   end
   if errors_mode == 'diagnostic' then
-    diagnostic.set(bufnr, name, provider.error_parser, output, ctx)
+    return diagnostic.set(bufnr, name, provider.error_parser, output, ctx)
   elseif errors_mode == 'quickfix' then
     local ok, diags = pcall(provider.error_parser, output, ctx)
     if ok and diags and #diags > 0 then
@@ -83,8 +97,10 @@ local function handle_errors(bufnr, name, provider, ctx, output)
       local win = vim.fn.win_getid()
       vim.cmd.cwindow()
       vim.fn.win_gotoid(win)
+      return #diags
     end
   end
+  return 0
 end
 
 ---@param bufnr integer
@@ -169,6 +185,7 @@ local function stop_watching(bufnr, s)
   s.watching = false
   M.stop(bufnr)
   stop_open_watcher(bufnr)
+  stop_output_watcher(bufnr)
   close_viewer(bufnr)
   s.viewer_open = nil
   if s.bwp_autocmd then
@@ -250,7 +267,11 @@ function M.compile(bufnr, name, provider, ctx, opts)
             return
           end
           stderr_acc[#stderr_acc + 1] = data
-          handle_errors(bufnr, name, provider, ctx, table.concat(stderr_acc))
+          local count = handle_errors(bufnr, name, provider, ctx, table.concat(stderr_acc))
+          if count > 0 and not s.has_errors then
+            s.has_errors = true
+            vim.notify('[preview.nvim]: compilation failed', vim.log.levels.ERROR)
+          end
         end),
       },
       vim.schedule_wrap(function(result)
@@ -263,6 +284,7 @@ function M.compile(bufnr, name, provider, ctx, opts)
         end
         if result.code ~= 0 then
           log.dbg('long-running process failed for buffer %d (exit code %d)', bufnr, result.code)
+          vim.notify('[preview.nvim]: compilation failed', vim.log.levels.ERROR)
           handle_errors(bufnr, name, provider, ctx, (result.stdout or '') .. (result.stderr or ''))
           vim.api.nvim_exec_autocmds('User', {
             pattern = 'PreviewCompileFailed',
@@ -325,10 +347,54 @@ function M.compile(bufnr, name, provider, ctx, opts)
       end
     end
 
+    if output_file ~= '' then
+      local out_dir = vim.fn.fnamemodify(output_file, ':h')
+      local out_name = vim.fn.fnamemodify(output_file, ':t')
+      stop_output_watcher(bufnr)
+      local ow = vim.uv.new_fs_event()
+      if ow then
+        s.output_watcher = ow
+        local last_mtime = 0
+        local stat = vim.uv.fs_stat(output_file)
+        if stat then
+          last_mtime = stat.mtime.sec
+        end
+        ow:start(
+          out_dir,
+          {},
+          vim.schedule_wrap(function(err, filename, _events)
+            if err or vim.fn.fnamemodify(filename or '', ':t') ~= out_name then
+              return
+            end
+            if not vim.api.nvim_buf_is_valid(bufnr) then
+              stop_output_watcher(bufnr)
+              return
+            end
+            local new_stat = vim.uv.fs_stat(output_file)
+            if not (new_stat and new_stat.mtime.sec > last_mtime) then
+              return
+            end
+            last_mtime = new_stat.mtime.sec
+            log.dbg('output updated for buffer %d', bufnr)
+            vim.notify('[preview.nvim]: compilation complete', vim.log.levels.INFO)
+            stderr_acc = {}
+            s.has_errors = false
+            clear_errors(bufnr, provider)
+            vim.api.nvim_exec_autocmds('User', {
+              pattern = 'PreviewCompileSuccess',
+              data = { bufnr = bufnr, provider = name, output = output_file },
+            })
+          end)
+        )
+      end
+    end
+
     s.process = obj
     s.provider = name
     s.is_reload = true
+    s.has_errors = false
 
+    vim.notify('[preview.nvim]: compiling...', vim.log.levels.INFO)
     vim.api.nvim_exec_autocmds('User', {
       pattern = 'PreviewCompileStarted',
       data = { bufnr = bufnr, provider = name },
@@ -360,6 +426,7 @@ function M.compile(bufnr, name, provider, ctx, opts)
       end
       if result.code == 0 then
         log.dbg('compilation succeeded for buffer %d', bufnr)
+        vim.notify('[preview.nvim]: compilation complete', vim.log.levels.INFO)
         clear_errors(bufnr, provider)
         vim.api.nvim_exec_autocmds('User', {
           pattern = 'PreviewCompileSuccess',
@@ -385,6 +452,7 @@ function M.compile(bufnr, name, provider, ctx, opts)
         end
       else
         log.dbg('compilation failed for buffer %d (exit code %d)', bufnr, result.code)
+        vim.notify('[preview.nvim]: compilation failed', vim.log.levels.ERROR)
         handle_errors(bufnr, name, provider, ctx, (result.stdout or '') .. (result.stderr or ''))
         vim.api.nvim_exec_autocmds('User', {
           pattern = 'PreviewCompileFailed',
@@ -403,6 +471,7 @@ function M.compile(bufnr, name, provider, ctx, opts)
   s.provider = name
   s.is_reload = false
 
+  vim.notify('[preview.nvim]: compiling...', vim.log.levels.INFO)
   vim.api.nvim_exec_autocmds('User', {
     pattern = 'PreviewCompileStarted',
     data = { bufnr = bufnr, provider = name },
@@ -415,6 +484,7 @@ function M.stop(bufnr)
   if not s then
     return
   end
+  stop_output_watcher(bufnr)
   local obj = s.process
   if not obj then
     return
@@ -480,6 +550,7 @@ function M.toggle(bufnr, name, provider, ctx_builder)
     callback = function()
       M.stop(bufnr)
       stop_open_watcher(bufnr)
+      stop_output_watcher(bufnr)
       if not provider.detach then
         close_viewer(bufnr)
       end
@@ -512,7 +583,6 @@ function M.toggle(bufnr, name, provider, ctx_builder)
     log.dbg('watching buffer %d with provider "%s"', bufnr, name)
   end
 
-  vim.notify('[preview.nvim]: watching with "' .. name .. '"', vim.log.levels.INFO)
   M.compile(bufnr, name, provider, ctx_builder(bufnr))
 end
 
diff --git a/lua/preview/diagnostic.lua b/lua/preview/diagnostic.lua
index abd4105..62a5b45 100644
--- a/lua/preview/diagnostic.lua
+++ b/lua/preview/diagnostic.lua
@@ -15,21 +15,23 @@ end
 ---@param error_parser fun(output: string, ctx: preview.Context): preview.Diagnostic[]
 ---@param output string
 ---@param ctx preview.Context
+---@return integer
 function M.set(bufnr, name, error_parser, output, ctx)
   local ok, diagnostics = pcall(error_parser, output, ctx)
   if not ok then
     log.dbg('error_parser for "%s" failed: %s', name, diagnostics)
-    return
+    return 0
   end
   if not diagnostics or #diagnostics == 0 then
     log.dbg('error_parser for "%s" returned no diagnostics', name)
-    return
+    return 0
   end
   for _, d in ipairs(diagnostics) do
     d.source = d.source or name
   end
   vim.diagnostic.set(ns, bufnr, diagnostics)
   log.dbg('set %d diagnostics for buffer %d from provider "%s"', #diagnostics, bufnr, name)
+  return #diagnostics
 end
 
 ---@return integer
diff --git a/lua/preview/presets.lua b/lua/preview/presets.lua
index 1f333bf..6a3a000 100644
--- a/lua/preview/presets.lua
+++ b/lua/preview/presets.lua
@@ -224,7 +224,7 @@ M.markdown = {
   ft = 'markdown',
   cmd = { 'pandoc' },
   args = function(ctx)
-    return { ctx.file, '-s', '--embed-resources', '--mathml', '-o', ctx.output }
+    return { ctx.file, '-s', '--katex', '-o', ctx.output }
   end,
   output = function(ctx)
     return (ctx.file:gsub('%.md$', '.html'))
@@ -249,8 +249,7 @@ M.github = {
       'gfm',
       ctx.file,
       '-s',
-      '--embed-resources',
-      '--mathml',
+      '--katex',
       '--css',
       'https://cdn.jsdelivr.net/gh/pixelbrackets/gfm-stylesheet@master/dist/gfm.css',
       '-o',
diff --git a/spec/compiler_spec.lua b/spec/compiler_spec.lua
index 5b12cfb..61a03d5 100644
--- a/spec/compiler_spec.lua
+++ b/spec/compiler_spec.lua
@@ -55,6 +55,14 @@ describe('compiler', function()
         end,
       })
 
+      local notified = false
+      local orig = vim.notify
+      vim.notify = function(msg)
+        if msg:find('compiling') then
+          notified = true
+        end
+      end
+
       local provider = { cmd = { 'echo', 'ok' } }
       local ctx = {
         bufnr = bufnr,
@@ -64,7 +72,9 @@ describe('compiler', function()
       }
 
       compiler.compile(bufnr, 'echo', provider, ctx)
+      vim.notify = orig
       assert.is_true(fired)
+      assert.is_true(notified)
 
       vim.wait(2000, function()
         return process_done(bufnr)
@@ -269,6 +279,58 @@ describe('compiler', function()
     end)
   end)
 
+  describe('long-running notifications', function()
+    it('notifies failure on stderr diagnostics', function()
+      local bufnr = helpers.create_buffer({ 'hello' }, 'text')
+      vim.api.nvim_buf_set_name(bufnr, '/tmp/preview_test_longrun.txt')
+      vim.bo[bufnr].modified = false
+
+      local notified_fail = false
+      local orig = vim.notify
+      vim.notify = function(msg, level)
+        if msg:find('compilation failed') and level == vim.log.levels.ERROR then
+          notified_fail = true
+        end
+      end
+
+      local provider = {
+        cmd = { 'sh' },
+        reload = function()
+          return { 'sh', '-c', 'echo "error: bad input" >&2; sleep 60' }
+        end,
+        error_parser = function()
+          return {
+            { lnum = 0, col = 0, message = 'bad input', severity = vim.diagnostic.severity.ERROR },
+          }
+        end,
+      }
+      local ctx = {
+        bufnr = bufnr,
+        file = '/tmp/preview_test_longrun.txt',
+        root = '/tmp',
+        ft = 'text',
+      }
+
+      compiler.compile(bufnr, 'testprov', provider, ctx)
+
+      vim.wait(3000, function()
+        return notified_fail
+      end, 50)
+
+      vim.notify = orig
+      assert.is_true(notified_fail)
+
+      local s = compiler._test.state[bufnr]
+      assert.is_true(s.has_errors)
+
+      compiler.stop(bufnr)
+      vim.wait(2000, function()
+        return process_done(bufnr)
+      end, 50)
+      helpers.delete_buffer(bufnr)
+    end)
+  end)
+
   describe('stop', function()
     it('does nothing when no process is active', function()
       assert.has_no.errors(function()
diff --git a/spec/diagnostic_spec.lua b/spec/diagnostic_spec.lua
index 05ccc6d..0701952 100644
--- a/spec/diagnostic_spec.lua
+++ b/spec/diagnostic_spec.lua
@@ -124,5 +124,47 @@ describe('diagnostic', function()
       assert.are.equal(0, #diags)
       helpers.delete_buffer(bufnr)
     end)
+
+    it('returns count of diagnostics set', function()
+      local bufnr = helpers.create_buffer({ 'line1', 'line2' })
+
+      local parser = function()
+        return {
+          { lnum = 0, col = 0, message = 'err1', severity = vim.diagnostic.severity.ERROR },
+          { lnum = 1, col = 0, message = 'err2', severity = vim.diagnostic.severity.WARN },
+        }
+      end
+
+      local ctx = { bufnr = bufnr, file = '/tmp/test.typ', root = '/tmp', ft = 'typst' }
+      local count = diagnostic.set(bufnr, 'typst', parser, 'errors', ctx)
+      assert.are.equal(2, count)
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('returns 0 on parser failure', function()
+      local bufnr = helpers.create_buffer({ 'line1' })
+
+      local parser = function()
+        error('boom')
+      end
+
+      local ctx = { bufnr = bufnr, file = '/tmp/test.tex', root = '/tmp', ft = 'tex' }
+      local count = diagnostic.set(bufnr, 'latexmk', parser, 'error', ctx)
+      assert.are.equal(0, count)
+      helpers.delete_buffer(bufnr)
+    end)
+
+    it('returns 0 on empty diagnostics', function()
+      local bufnr = helpers.create_buffer({ 'line1' })
+
+      local parser = function()
+        return {}
+      end
+
+      local ctx = { bufnr = bufnr, file = '/tmp/test.tex', root = '/tmp', ft = 'tex' }
+      local count = diagnostic.set(bufnr, 'latexmk', parser, 'error', ctx)
+      assert.are.equal(0, count)
+      helpers.delete_buffer(bufnr)
+    end)
   end)
 end)
diff --git a/spec/presets_spec.lua b/spec/presets_spec.lua
index 573b1ef..7d86dac 100644
--- a/spec/presets_spec.lua
+++ b/spec/presets_spec.lua
@@ -294,13 +294,10 @@ describe('presets', function()
       assert.are.same({ 'pandoc' }, presets.markdown.cmd)
     end)
 
-    it('returns args with standalone, embed-resources, and mathml flags', function()
+    it('returns args with standalone and katex flags', function()
       local args = presets.markdown.args(md_ctx)
       assert.is_table(args)
-      assert.are.same(
-        { '/tmp/document.md', '-s', '--embed-resources', '--mathml', '-o', '/tmp/document.html' },
-        args
-      )
+      assert.are.same({ '/tmp/document.md', '-s', '--katex', '-o', '/tmp/document.html' }, args)
     end)
 
     it('returns html output path', function()
@@ -382,7 +379,7 @@ describe('presets', function()
       assert.are.same({ 'pandoc' }, presets.github.cmd)
     end)
 
-    it('returns args with standalone, embed-resources, mathml, and css flags', function()
+    it('returns args with standalone, katex, and css flags', function()
       local args = presets.github.args(md_ctx)
       assert.is_table(args)
       assert.are.same({
@@ -390,8 +387,7 @@ describe('presets', function()
         'gfm',
         '/tmp/document.md',
         '-s',
-        '--embed-resources',
-        '--mathml',
+        '--katex',
         '--css',
         'https://cdn.jsdelivr.net/gh/pixelbrackets/gfm-stylesheet@master/dist/gfm.css',
         '-o',