diff --git a/app/web/errors/error_classifier.rb b/app/web/errors/error_classifier.rb
index 8d604262..46f80a69 100644
--- a/app/web/errors/error_classifier.rb
+++ b/app/web/errors/error_classifier.rb
@@ -19,7 +19,7 @@ module ErrorClassifier # rubocop:disable Metrics/ModuleLength
       ##
       # Gem strategy attempts plus expanded transport telemetry for feed Observability / headers.
       Diagnostics = Data.define(
-        :strategy_attempts, :request_id, :strategy_used, :render_ms, :error_category
+        :strategy_attempts, :request_id, :strategy_used, :render_ms, :error_category, :timeout_phase
       ) do
         class << self
           # @return [Html2rss::Web::ErrorClassifier::Diagnostics]
@@ -28,12 +28,20 @@ def empty
           end
 
           # Digs strategy attempts from the exception cause chain.
+          # Prefer +timeout_phase+ from transport_meta; else from +RequestTimedOut+ in the chain.
           #
           # @param error [Exception, nil]
           # @return [Html2rss::Web::ErrorClassifier::Diagnostics]
           def from_error(error)
-            with_attempts = ErrorClassifier.error_chain(error).find { it.respond_to?(:attempts) }
-            from_attempts(with_attempts ? Array(with_attempts.attempts) : [])
+            chain = ErrorClassifier.error_chain(error)
+            with_attempts = chain.find { it.respond_to?(:attempts) }
+            list = with_attempts ? Array(with_attempts.attempts) : []
+            fields = transport_fields(list)
+            fields[:timeout_phase] ||= timeout_phase_from_chain(chain)
+
+            return EMPTY_DIAGNOSTICS if list.empty? && fields.values.all?(&:nil?)
+
+            new(strategy_attempts: list, **fields)
           end
 
           # Expands attempt hashes into transport fields (single dig algorithm).
@@ -57,10 +65,23 @@ def transport_fields(attempts)
               request_id: dig_meta(meta, :request_id),
               strategy_used: dig_meta(meta, :strategy_used),
               render_ms: dig_meta(meta, :render_ms),
-              error_category: dig_meta(meta, :error_category)
+              error_category: dig_meta(meta, :error_category),
+              timeout_phase: dig_meta(meta, :timeout_phase)
             }
           end
 
+          # @param chain [Array<Exception>]
+          # @return [Object, nil]
+          def timeout_phase_from_chain(chain)
+            return unless defined?(::Html2rss::RequestService::RequestTimedOut)
+
+            timed_out = chain.find { it.is_a?(::Html2rss::RequestService::RequestTimedOut) }
+            return unless timed_out
+            return unless timed_out.respond_to?(:timeout_phase)
+
+            timed_out.timeout_phase
+          end
+
           # @param meta [Hash, nil]
           # @param key [Symbol]
           # @return [Object, nil]
@@ -76,7 +97,7 @@ def dig_meta(meta, key)
         # @return [Hash{Symbol=>Object}]
         def to_h
           details = strategy_attempts.empty? ? {} : { strategy_attempts: strategy_attempts }
-          %i[request_id strategy_used render_ms error_category].each do |key|
+          %i[request_id strategy_used render_ms error_category timeout_phase].each do |key|
             val = public_send(key)
             details[key] = val if val
           end
@@ -88,7 +109,8 @@ def to_h
         request_id: nil,
         strategy_used: nil,
         render_ms: nil,
-        error_category: nil
+        error_category: nil,
+        timeout_phase: nil
       ).freeze
 
       ##
@@ -213,8 +235,19 @@ def initialize(decision)
            defined?(::Html2rss::RequestService::BotasaurusConnectionFailed) &&
              c.any?(::Html2rss::RequestService::BotasaurusConnectionFailed)
          }, SCRAPER_UNAVAILABLE],
+        [lambda { |c, _|
+           # queue/boot = our capacity or Chromium — not the target site.
+           return false unless defined?(::Html2rss::RequestService::RequestTimedOut)
+
+           timed_out = c.find { it.is_a?(::Html2rss::RequestService::RequestTimedOut) }
+           return false unless timed_out
+
+           phase = timed_out.respond_to?(:timeout_phase) ? timed_out.timeout_phase : nil
+           %w[queue boot].include?(phase)
+         }, SERVICE_UNAVAILABLE],
         [lambda { |c, _|
            # Gem wall-clock timeout (Botasaurus 504 / Faraday timeout) — not Timeout::Error.
+           # work / nil (transport hop) → site-shaped 504.
            defined?(::Html2rss::RequestService::RequestTimedOut) &&
              c.any?(::Html2rss::RequestService::RequestTimedOut)
          }, GATEWAY_TIMEOUT],
diff --git a/docs/README.md b/docs/README.md
index 480eb526..46f8a4cd 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -239,7 +239,7 @@ Default `docker-compose.yml` aligns botasaurus-scrape-api, the html2rss gem clie
 | `HTML2RSS_TOTAL_TIMEOUT_SECONDS` | html2rss-web | `50` | Feed build budget (scrape + extraction) |
 | `RACK_TIMEOUT_SERVICE_TIMEOUT` | html2rss-web | `55` | Rack outer wall |
 
-When triaging `GATEWAY_TIMEOUT` or `error_category:timeout`, confirm both projects use this ladder. Scraper terminal timeouts near **45s** with web failures near **50–55s** indicate aligned budgets; scraper failures near **20–25s** while web waits longer usually mean stale `SCRAPE_*` / `BOTASAURUS_*` env on one side.
+When triaging `GATEWAY_TIMEOUT`, capacity-shaped `SERVICE_UNAVAILABLE` (queue/boot), or `error_category:timeout`, confirm both projects use this ladder. Scraper terminal timeouts near **45s** with web failures near **50–55s** indicate aligned budgets; scraper failures near **20–25s** while web waits longer usually mean stale `SCRAPE_*` / `BOTASAURUS_*` env on one side. Split queue/boot timeouts from work timeouts before blaming the ladder (see **Alert baselines**).
 
 ## Sentry Runbook
 
@@ -255,9 +255,10 @@ Start triage from the newest `feed.create`, `feed.render`, and `request.error` e
 2. **Correlate** — copy `request_id` from one issue and search the other project.
 3. **Decision tree**
    - `SCRAPER_UNAVAILABLE` / `navigation_error` → scraper down or unreachable
+   - `SERVICE_UNAVAILABLE` with scraper `timeout_phase` `queue` or `boot` → our capacity (queue backlog) or Chromium boot (RAM/shm/prewarm) — not the target site
    - `challenge_block` (scraper) or `BLOCKED_SURFACE` (web) → site blocked automation (product signal)
    - `EXTRACTION_EMPTY` → selectors/config (product signal)
-   - `GATEWAY_TIMEOUT` / `timeout` → slow target, or timeout ladder mismatch (see **Compose timeout ladder**)
+   - `GATEWAY_TIMEOUT` / `timeout` with `timeout_phase` `work` (or nil transport hop) → slow or hostile target, or timeout ladder mismatch (see **Compose timeout ladder**)
 
 ### Alert baselines
 
@@ -266,12 +267,15 @@ After baseline traffic, configure per project:
 **Project B (scraper)**
 
 - P0: `error_category:navigation_error` above baseline
-- P0: `error_category:timeout` sustained spike
-- Metric: `scrape.challenge_block` anomaly (product signal)
+- P0: sustained `error_category:timeout` with `timeout_phase` in `{queue, boot}` (capacity / Chromium) — scale workers or check RAM/shm/prewarm
+- P1: sustained `error_category:timeout` with `timeout_phase:work` (slow or hostile targets) — distinct from capacity
+- Metric: `scrape.challenge_block` anomaly (product signal; not a timeout)
 
 **Project A (web)**
 
 - P0: `error_code:SCRAPER_UNAVAILABLE` sustained
+- P0: `error_code:SERVICE_UNAVAILABLE` sustained when correlated with scraper queue/boot timeouts (capacity)
+- P1: `error_code:GATEWAY_TIMEOUT` sustained (slow targets / ladder mismatch) — do not conflate with capacity
 - P0: `request.error` spike with `kind:server`
 
 ### Dashboard baselines
diff --git a/spec/html2rss/web/error_classifier_spec.rb b/spec/html2rss/web/error_classifier_spec.rb
index 1ad2629d..7c0a0937 100644
--- a/spec/html2rss/web/error_classifier_spec.rb
+++ b/spec/html2rss/web/error_classifier_spec.rb
@@ -19,6 +19,17 @@ def initialize(attempts:)
     end)
   end
 
+  def stub_request_timed_out
+    stub_const('Html2rss::RequestService::RequestTimedOut', Class.new(Html2rss::Error) do
+      def initialize(message = nil, timeout_phase: nil)
+        @timeout_phase = timeout_phase
+        super(message)
+      end
+
+      attr_reader :timeout_phase
+    end)
+  end
+
   describe '.classify' do
     it 'returns a carried Decision without remapping' do
       decided = described_class::DecidedError.new(described_class::BLOCKED_SURFACE)
@@ -85,14 +96,35 @@ def initialize(attempts:)
     end
 
     it 'returns gateway timeout for RequestTimedOut (Botasaurus/Faraday wall-clock)' do
-      stub_const('Html2rss::RequestService::RequestTimedOut', Class.new(Html2rss::Error))
+      stub_request_timed_out
       error = Html2rss::RequestService::RequestTimedOut.new('Botasaurus scrape timed out')
 
       expect(described_class.classify(error)).to eq(described_class::GATEWAY_TIMEOUT)
     end
 
+    it 'returns gateway timeout for RequestTimedOut with timeout_phase work' do
+      stub_request_timed_out
+      error = Html2rss::RequestService::RequestTimedOut.new('work timed out', timeout_phase: 'work')
+
+      expect(described_class.classify(error)).to eq(described_class::GATEWAY_TIMEOUT)
+    end
+
+    it 'returns service unavailable for RequestTimedOut with timeout_phase queue' do
+      stub_request_timed_out
+      error = Html2rss::RequestService::RequestTimedOut.new('queued too long', timeout_phase: 'queue')
+
+      expect(described_class.classify(error)).to eq(described_class::SERVICE_UNAVAILABLE)
+    end
+
+    it 'returns service unavailable for RequestTimedOut with timeout_phase boot' do
+      stub_request_timed_out
+      error = Html2rss::RequestService::RequestTimedOut.new('browser boot timed out', timeout_phase: 'boot')
+
+      expect(described_class.classify(error)).to eq(described_class::SERVICE_UNAVAILABLE)
+    end
+
     it 'detects RequestTimedOut through Exception#cause' do
-      stub_const('Html2rss::RequestService::RequestTimedOut', Class.new(Html2rss::Error))
+      stub_request_timed_out
       root = Html2rss::RequestService::RequestTimedOut.new('timed out')
       wrapped = StandardError.new('wrapped')
       allow(wrapped).to receive(:cause).and_return(root)
@@ -100,6 +132,22 @@ def initialize(attempts:)
       expect(described_class.classify(wrapped)).to eq(described_class::GATEWAY_TIMEOUT)
     end
 
+    it 'maps queue timeout_phase through Exception#cause to service unavailable' do
+      stub_request_timed_out
+      root = Html2rss::RequestService::RequestTimedOut.new('capacity', timeout_phase: 'queue')
+      wrapped = StandardError.new('wrapped')
+      allow(wrapped).to receive(:cause).and_return(root)
+
+      expect(described_class.classify(wrapped)).to eq(described_class::SERVICE_UNAVAILABLE)
+    end
+
+    it 'keeps gateway timeout when RequestTimedOut omits timeout_phase reader' do
+      stub_const('Html2rss::RequestService::RequestTimedOut', Class.new(Html2rss::Error))
+      error = Html2rss::RequestService::RequestTimedOut.new('legacy timed out')
+
+      expect(described_class.classify(error)).to eq(described_class::GATEWAY_TIMEOUT)
+    end
+
     it 'returns internal server error decision for unrelated errors' do
       expect(described_class.classify(StandardError.new('boom'))).to eq(described_class::INTERNAL_SERVER_ERROR)
     end
@@ -170,7 +218,12 @@ def initialize(attempts:)
           {
             strategy: :faraday,
             items_count: 0,
-            transport_meta: { 'request_id' => 'req-123', 'render_ms' => 45, 'strategy_used' => 'faraday' }
+            transport_meta: {
+              'request_id' => 'req-123',
+              'render_ms' => 45,
+              'strategy_used' => 'faraday',
+              'timeout_phase' => 'work'
+            }
           }
         ]
       )
@@ -178,16 +231,45 @@ def initialize(attempts:)
 
     it 'extracts strategy attempts and transport meta when present', :aggregate_failures do
       diagnostics = described_class::Diagnostics.from_error(diagnostic_error)
+      expect(diagnostics).to have_attributes(
+        request_id: 'req-123', render_ms: 45, strategy_used: 'faraday', timeout_phase: 'work'
+      )
       expect(diagnostics.strategy_attempts.size).to eq(1)
-      expect(diagnostics.request_id).to eq('req-123')
-      expect(diagnostics.render_ms).to eq(45)
-      expect(diagnostics.strategy_used).to eq('faraday')
       expect(diagnostics.to_h).to include(
         strategy_attempts: diagnostics.strategy_attempts,
-        request_id: 'req-123',
-        render_ms: 45,
-        strategy_used: 'faraday'
+        request_id: 'req-123', render_ms: 45, strategy_used: 'faraday', timeout_phase: 'work'
+      )
+    end
+
+    it 'prefers transport_meta timeout_phase over RequestTimedOut on the chain' do
+      stub_request_timed_out
+      timed_out = Html2rss::RequestService::RequestTimedOut.new('queued', timeout_phase: 'queue')
+      allow(diagnostic_error).to receive(:cause).and_return(timed_out)
+
+      expect(described_class::Diagnostics.from_error(diagnostic_error).timeout_phase).to eq('work')
+    end
+
+    it 'falls back to RequestTimedOut#timeout_phase when transport_meta omits it' do
+      stub_request_timed_out
+      klass = stub_no_feed_items_extracted_with_attempts
+      error = klass.new(
+        attempts: [{ strategy: :botasaurus, items_count: 0,
+                     transport_meta: { 'request_id' => 'req-9', 'error_category' => 'timeout' } }]
+      )
+      allow(error).to receive(:cause).and_return(
+        Html2rss::RequestService::RequestTimedOut.new('capacity', timeout_phase: 'boot')
       )
+
+      expect(described_class::Diagnostics.from_error(error)).to have_attributes(
+        request_id: 'req-9', error_category: 'timeout', timeout_phase: 'boot'
+      )
+    end
+
+    it 'emits timeout_phase from RequestTimedOut when attempts are absent' do
+      stub_request_timed_out
+      error = Html2rss::RequestService::RequestTimedOut.new('queued too long', timeout_phase: 'queue')
+
+      expect(described_class::Diagnostics.from_error(error).to_h).to eq(timeout_phase: 'queue')
     end
 
     it 'returns empty diagnostics when no attempts are present' do
diff --git a/spec/html2rss/web/sentry_ops_spec.rb b/spec/html2rss/web/sentry_ops_spec.rb
index 0ddc8416..cb0ba8ad 100644
--- a/spec/html2rss/web/sentry_ops_spec.rb
+++ b/spec/html2rss/web/sentry_ops_spec.rb
@@ -15,7 +15,8 @@
       request_id: 'req-scrape-42',
       strategy_used: 'botasaurus',
       render_ms: 12_345,
-      error_category: 'timeout'
+      error_category: 'timeout',
+      timeout_phase: nil
     )
   end
   let(:context) do