diff --git a/shared/static/scripts/sx-ref.js b/shared/static/scripts/sx-ref.js
index 8ca8260..4db4434 100644
--- a/shared/static/scripts/sx-ref.js
+++ b/shared/static/scripts/sx-ref.js
@@ -609,6 +609,14 @@
     return result;
   }
 
+  function componentIoRefs(c) {
+    return c.ioRefs ? c.ioRefs.slice() : [];
+  }
+
+  function componentSetIoRefs(c, refs) {
+    c.ioRefs = refs;
+  }
+
 
   // =========================================================================
   // Platform interface — Parser
@@ -2456,6 +2464,43 @@ callExpr.push(dictGet(kwargs, k)); } }
   return classes;
 })(); };
 
+  // scan-io-refs-walk
+  var scanIoRefsWalk = function(node, ioNames, refs) { return (isSxTruthy((typeOf(node) == "symbol")) ? (function() {
+  var name = symbolName(node);
+  return (isSxTruthy(contains(ioNames, name)) ? (isSxTruthy(!contains(refs, name)) ? append_b(refs, name) : NIL) : NIL);
+})() : (isSxTruthy((typeOf(node) == "list")) ? forEach(function(item) { return scanIoRefsWalk(item, ioNames, refs); }, node) : (isSxTruthy((typeOf(node) == "dict")) ? forEach(function(key) { return scanIoRefsWalk(dictGet(node, key), ioNames, refs); }, keys(node)) : NIL))); };
+
+  // scan-io-refs
+  var scanIoRefs = function(node, ioNames) { return (function() {
+  var refs = [];
+  scanIoRefsWalk(node, ioNames, refs);
+  return refs;
+})(); };
+
+  // transitive-io-refs-walk
+  var transitiveIoRefsWalk = function(n, seen, allRefs, env, ioNames) { return (isSxTruthy(!contains(seen, n)) ? (append_b(seen, n), (function() {
+  var val = envGet(env, n);
+  return (isSxTruthy((typeOf(val) == "component")) ? (forEach(function(ref) { return (isSxTruthy(!contains(allRefs, ref)) ? append_b(allRefs, ref) : NIL); }, scanIoRefs(componentBody(val), ioNames)), forEach(function(dep) { return transitiveIoRefsWalk(dep, seen, allRefs, env, ioNames); }, scanRefs(componentBody(val)))) : (isSxTruthy((typeOf(val) == "macro")) ? (forEach(function(ref) { return (isSxTruthy(!contains(allRefs, ref)) ? append_b(allRefs, ref) : NIL); }, scanIoRefs(macroBody(val), ioNames)), forEach(function(dep) { return transitiveIoRefsWalk(dep, seen, allRefs, env, ioNames); }, scanRefs(macroBody(val)))) : NIL));
+})()) : NIL); };
+
+  // transitive-io-refs
+  var transitiveIoRefs = function(name, env, ioNames) { return (function() {
+  var allRefs = [];
+  var seen = [];
+  var key = (isSxTruthy(startsWith(name, "~")) ? name : (String("~") + String(name)));
+  transitiveIoRefsWalk(key, seen, allRefs, env, ioNames);
+  return allRefs;
+})(); };
+
+  // compute-all-io-refs
+  var computeAllIoRefs = function(env, ioNames) { return forEach(function(name) { return (function() {
+  var val = envGet(env, name);
+  return (isSxTruthy((typeOf(val) == "component")) ? componentSetIoRefs(val, transitiveIoRefs(name, env, ioNames)) : NIL);
+})(); }, envComponents(env)); };
+
+  // component-pure?
+  var componentPure_p = function(name, env, ioNames) { return isEmpty(transitiveIoRefs(name, env, ioNames)); };
+
 
   // =========================================================================
   // Platform interface — DOM adapter (browser-only)
@@ -3626,6 +3671,10 @@ callExpr.push(dictGet(kwargs, k)); } }
     componentsNeeded: componentsNeeded,
     pageComponentBundle: pageComponentBundle,
     pageCssClasses: pageCssClasses,
+    scanIoRefs: scanIoRefs,
+    transitiveIoRefs: transitiveIoRefs,
+    computeAllIoRefs: computeAllIoRefs,
+    componentPure_p: componentPure_p,
     _version: "ref-2.0 (boot+cssx+dom+engine+html+orchestration+parser+sx, bootstrap-compiled)"
   };
 
@@ -3649,4 +3698,4 @@ callExpr.push(dictGet(kwargs, k)); } }
   if (typeof module !== "undefined" && module.exports) module.exports = Sx;
   else global.Sx = Sx;
 
-})(typeof globalThis !== "undefined" ? globalThis : typeof window !== "undefined" ? window : this);
\ No newline at end of file
+})(typeof globalThis !== "undefined" ? globalThis : typeof window !== "undefined" ? window : this);
diff --git a/shared/sx/async_eval.py b/shared/sx/async_eval.py
index c9827d2..de0950d 100644
--- a/shared/sx/async_eval.py
+++ b/shared/sx/async_eval.py
@@ -1332,8 +1332,9 @@ async def _aser(expr: Any, env: dict[str, Any], ctx: RequestContext) -> Any:
             if isinstance(val, Macro):
                 expanded = _expand_macro(val, expr[1:], env)
                 return await _aser(expanded, env, ctx)
-            if isinstance(val, Component) and _expand_components.get():
-                return await _aser_component(val, expr[1:], env, ctx)
+            if isinstance(val, Component):
+                if _expand_components.get() or not val.is_pure:
+                    return await _aser_component(val, expr[1:], env, ctx)
             return await _aser_call(name, expr[1:], env, ctx)
 
         # Serialize-mode special/HO forms (checked BEFORE HTML_TAGS
diff --git a/shared/sx/deps.py b/shared/sx/deps.py
index 488fb4c..ceeee4a 100644
--- a/shared/sx/deps.py
+++ b/shared/sx/deps.py
@@ -68,6 +68,62 @@ def _compute_all_deps_fallback(env: dict[str, Any]) -> None:
             val.deps = _transitive_deps_fallback(key, env)
 
 
+def _scan_io_refs_fallback(node: Any, io_names: set[str]) -> set[str]:
+    """Scan an AST node for references to IO primitive names."""
+    refs: set[str] = set()
+    _walk_io(node, io_names, refs)
+    return refs
+
+
+def _walk_io(node: Any, io_names: set[str], refs: set[str]) -> None:
+    if isinstance(node, Symbol):
+        if node.name in io_names:
+            refs.add(node.name)
+        return
+    if isinstance(node, list):
+        for item in node:
+            _walk_io(item, io_names, refs)
+        return
+    if isinstance(node, dict):
+        for v in node.values():
+            _walk_io(v, io_names, refs)
+        return
+
+
+def _transitive_io_refs_fallback(
+    name: str, env: dict[str, Any], io_names: set[str]
+) -> set[str]:
+    """Compute transitive IO primitive references for a component."""
+    all_refs: set[str] = set()
+    seen: set[str] = set()
+
+    def walk(n: str) -> None:
+        if n in seen:
+            return
+        seen.add(n)
+        val = env.get(n)
+        if isinstance(val, Component):
+            all_refs.update(_scan_io_refs_fallback(val.body, io_names))
+            for dep in _scan_ast(val.body):
+                walk(dep)
+        elif isinstance(val, Macro):
+            all_refs.update(_scan_io_refs_fallback(val.body, io_names))
+            for dep in _scan_ast(val.body):
+                walk(dep)
+
+    key = name if name.startswith("~") else f"~{name}"
+    walk(key)
+    return all_refs
+
+
+def _compute_all_io_refs_fallback(
+    env: dict[str, Any], io_names: set[str]
+) -> None:
+    for key, val in env.items():
+        if isinstance(val, Component):
+            val.io_refs = _transitive_io_refs_fallback(key, env, io_names)
+
+
 def _scan_components_from_sx_fallback(source: str) -> set[str]:
     import re
     return {f"~{m}" for m in re.findall(r'\(~([a-zA-Z_][a-zA-Z0-9_\-]*)', source)}
@@ -131,3 +187,27 @@ def components_needed(page_sx: str, env: dict[str, Any]) -> set[str]:
         from .ref.sx_ref import components_needed as _ref_cn
         return set(_ref_cn(page_sx, env))
     return _components_needed_fallback(page_sx, env)
+
+
+def compute_all_io_refs(env: dict[str, Any], io_names: set[str]) -> None:
+    """Compute and cache transitive IO refs for all Component entries in *env*."""
+    if _use_ref():
+        from .ref.sx_ref import compute_all_io_refs as _ref_cio
+        _ref_cio(env, list(io_names))
+        return
+    _compute_all_io_refs_fallback(env, io_names)
+
+
+def get_all_io_names() -> set[str]:
+    """Build the complete set of IO primitive names from all boundary tiers.
+
+    Includes: core IO (primitives_io.py handlers), plus all page helper names
+    from every service boundary.
+    """
+    from .primitives_io import IO_PRIMITIVES
+    from .boundary import declared_helpers
+
+    names = set(IO_PRIMITIVES)
+    for _svc, helper_names in declared_helpers().items():
+        names.update(helper_names)
+    return names
diff --git a/shared/sx/jinja_bridge.py b/shared/sx/jinja_bridge.py
index 71533d1..9f44cd4 100644
--- a/shared/sx/jinja_bridge.py
+++ b/shared/sx/jinja_bridge.py
@@ -204,8 +204,9 @@ def register_components(sx_source: str) -> None:
             val.css_classes = set(all_classes)
 
     # Recompute transitive deps for all components (cheap — just AST walking)
-    from .deps import compute_all_deps
+    from .deps import compute_all_deps, compute_all_io_refs, get_all_io_names
     compute_all_deps(_COMPONENT_ENV)
+    compute_all_io_refs(_COMPONENT_ENV, get_all_io_names())
 
     _compute_component_hash()
 
diff --git a/shared/sx/ref/bootstrap_js.py b/shared/sx/ref/bootstrap_js.py
index 3efe0f0..160bbc2 100644
--- a/shared/sx/ref/bootstrap_js.py
+++ b/shared/sx/ref/bootstrap_js.py
@@ -502,9 +502,17 @@ class JSEmitter:
             "component-deps": "componentDeps",
             "component-set-deps!": "componentSetDeps",
             "component-css-classes": "componentCssClasses",
+            "component-io-refs": "componentIoRefs",
+            "component-set-io-refs!": "componentSetIoRefs",
             "env-components": "envComponents",
             "regex-find-all": "regexFindAll",
             "scan-css-classes": "scanCssClasses",
+            # deps.sx IO detection
+            "scan-io-refs": "scanIoRefs",
+            "scan-io-refs-walk": "scanIoRefsWalk",
+            "transitive-io-refs": "transitiveIoRefs",
+            "compute-all-io-refs": "computeAllIoRefs",
+            "component-pure?": "componentPure_p",
         }
         if name in RENAMES:
             return RENAMES[name]
@@ -1904,6 +1912,14 @@ PLATFORM_DEPS_JS = '''
     }
     return result;
   }
+
+  function componentIoRefs(c) {
+    return c.ioRefs ? c.ioRefs.slice() : [];
+  }
+
+  function componentSetIoRefs(c, refs) {
+    c.ioRefs = refs;
+  }
 '''
 
 PLATFORM_PARSER_JS = r"""
@@ -3081,6 +3097,10 @@ def public_api_js(has_html, has_sx, has_dom, has_engine, has_orch, has_cssx, has
         api_lines.append('    componentsNeeded: componentsNeeded,')
         api_lines.append('    pageComponentBundle: pageComponentBundle,')
         api_lines.append('    pageCssClasses: pageCssClasses,')
+        api_lines.append('    scanIoRefs: scanIoRefs,')
+        api_lines.append('    transitiveIoRefs: transitiveIoRefs,')
+        api_lines.append('    computeAllIoRefs: computeAllIoRefs,')
+        api_lines.append('    componentPure_p: componentPure_p,')
 
     api_lines.append(f'    _version: "{version}"')
     api_lines.append('  };')
diff --git a/shared/sx/ref/bootstrap_py.py b/shared/sx/ref/bootstrap_py.py
index 01630a2..b98f2de 100644
--- a/shared/sx/ref/bootstrap_py.py
+++ b/shared/sx/ref/bootstrap_py.py
@@ -247,9 +247,17 @@ class PyEmitter:
             "component-deps": "component_deps",
             "component-set-deps!": "component_set_deps",
             "component-css-classes": "component_css_classes",
+            "component-io-refs": "component_io_refs",
+            "component-set-io-refs!": "component_set_io_refs",
             "env-components": "env_components",
             "regex-find-all": "regex_find_all",
             "scan-css-classes": "scan_css_classes",
+            # deps.sx IO detection
+            "scan-io-refs": "scan_io_refs",
+            "scan-io-refs-walk": "scan_io_refs_walk",
+            "transitive-io-refs": "transitive_io_refs",
+            "compute-all-io-refs": "compute_all_io_refs",
+            "component-pure?": "component_pure_p",
         }
         if name in RENAMES:
             return RENAMES[name]
@@ -1982,6 +1990,14 @@ PLATFORM_DEPS_PY = (
     '    for m in _re.finditer(r\';;\\s*@css\\s+(.+)\', source):\n'
     '        classes.update(m.group(1).split())\n'
     '    return list(classes)\n'
+    '\n'
+    'def component_io_refs(c):\n'
+    '    """Return cached IO refs list for a component (may be empty)."""\n'
+    '    return list(c.io_refs) if hasattr(c, "io_refs") and c.io_refs else []\n'
+    '\n'
+    'def component_set_io_refs(c, refs):\n'
+    '    """Cache IO refs on a component."""\n'
+    '    c.io_refs = set(refs) if not isinstance(refs, set) else refs\n'
 )
 
 
diff --git a/shared/sx/ref/deps.sx b/shared/sx/ref/deps.sx
index c0ff265..10bc059 100644
--- a/shared/sx/ref/deps.sx
+++ b/shared/sx/ref/deps.sx
@@ -208,6 +208,112 @@
       classes)))
 
 
+;; --------------------------------------------------------------------------
+;; 8. IO detection — scan component ASTs for IO primitive references
+;; --------------------------------------------------------------------------
+;; Extends the dependency walker to detect references to IO primitives.
+;; IO names are provided by the host (from boundary.sx declarations).
+;; A component is "pure" if it (transitively) references no IO primitives.
+;;
+;; Platform interface additions:
+;;   (component-io-refs c)        → cached IO ref list (may be empty)
+;;   (component-set-io-refs! c r) → cache IO refs on component
+
+(define scan-io-refs-walk
+  (fn (node io-names refs)
+    (cond
+      ;; Symbol → check if name is in the IO set
+      (= (type-of node) "symbol")
+        (let ((name (symbol-name node)))
+          (when (contains? io-names name)
+            (when (not (contains? refs name))
+              (append! refs name))))
+
+      ;; List → recurse into all elements
+      (= (type-of node) "list")
+        (for-each (fn (item) (scan-io-refs-walk item io-names refs)) node)
+
+      ;; Dict → recurse into values
+      (= (type-of node) "dict")
+        (for-each (fn (key) (scan-io-refs-walk (dict-get node key) io-names refs))
+                  (keys node))
+
+      ;; Literals → no IO refs
+      :else nil)))
+
+
+(define scan-io-refs
+  (fn (node io-names)
+    (let ((refs (list)))
+      (scan-io-refs-walk node io-names refs)
+      refs)))
+
+
+;; --------------------------------------------------------------------------
+;; 9. Transitive IO refs — follow component deps and union IO refs
+;; --------------------------------------------------------------------------
+
+(define transitive-io-refs-walk
+  (fn (n seen all-refs env io-names)
+    (when (not (contains? seen n))
+      (append! seen n)
+      (let ((val (env-get env n)))
+        (cond
+          (= (type-of val) "component")
+            (do
+              ;; Scan this component's body for IO refs
+              (for-each
+                (fn (ref)
+                  (when (not (contains? all-refs ref))
+                    (append! all-refs ref)))
+                (scan-io-refs (component-body val) io-names))
+              ;; Recurse into component deps
+              (for-each
+                (fn (dep) (transitive-io-refs-walk dep seen all-refs env io-names))
+                (scan-refs (component-body val))))
+
+          (= (type-of val) "macro")
+            (do
+              (for-each
+                (fn (ref)
+                  (when (not (contains? all-refs ref))
+                    (append! all-refs ref)))
+                (scan-io-refs (macro-body val) io-names))
+              (for-each
+                (fn (dep) (transitive-io-refs-walk dep seen all-refs env io-names))
+                (scan-refs (macro-body val))))
+
+          :else nil)))))
+
+
+(define transitive-io-refs
+  (fn (name env io-names)
+    (let ((all-refs (list))
+          (seen (list))
+          (key (if (starts-with? name "~") name (str "~" name))))
+      (transitive-io-refs-walk key seen all-refs env io-names)
+      all-refs)))
+
+
+;; --------------------------------------------------------------------------
+;; 10. Compute IO refs for all components in an environment
+;; --------------------------------------------------------------------------
+
+(define compute-all-io-refs
+  (fn (env io-names)
+    (for-each
+      (fn (name)
+        (let ((val (env-get env name)))
+          (when (= (type-of val) "component")
+            (component-set-io-refs! val (transitive-io-refs name env io-names)))))
+      (env-components env))))
+
+
+(define component-pure?
+  (fn (name env io-names)
+    (empty? (transitive-io-refs name env io-names))))
+
+
 ;; --------------------------------------------------------------------------
 ;; Platform interface summary
 ;; --------------------------------------------------------------------------
@@ -223,6 +329,8 @@
 ;;   (component-deps c)       → cached deps list (may be empty)
 ;;   (component-set-deps! c d)→ cache deps on component
 ;;   (component-css-classes c)→ pre-scanned CSS class list
+;;   (component-io-refs c)       → cached IO ref list (may be empty)
+;;   (component-set-io-refs! c r)→ cache IO refs on component
 ;;   (macro-body m)           → AST body of macro
 ;;   (env-components env)     → list of component names in env
 ;;   (regex-find-all pat src) → list of capture group matches
diff --git a/shared/sx/ref/sx_ref.py b/shared/sx/ref/sx_ref.py
index 64a250c..1cf606d 100644
--- a/shared/sx/ref/sx_ref.py
+++ b/shared/sx/ref/sx_ref.py
@@ -917,6 +917,14 @@ def scan_css_classes(source):
         classes.update(m.group(1).split())
     return list(classes)
 
+def component_io_refs(c):
+    """Return cached IO refs list for a component (may be empty)."""
+    return list(c.io_refs) if hasattr(c, "io_refs") and c.io_refs else []
+
+def component_set_io_refs(c, refs):
+    """Cache IO refs on a component."""
+    c.io_refs = set(refs) if not isinstance(refs, set) else refs
+
 
 # === Transpiled from eval ===
 
@@ -1210,6 +1218,24 @@ page_component_bundle = lambda page_source, env: components_needed(page_source,
 # page-css-classes
 page_css_classes = lambda page_source, env: (lambda needed: (lambda classes: _sx_begin(for_each(lambda name: (lambda val: (for_each(lambda cls: (_sx_append(classes, cls) if sx_truthy((not sx_truthy(contains_p(classes, cls)))) else NIL), component_css_classes(val)) if sx_truthy((type_of(val) == 'component')) else NIL))(env_get(env, name)), needed), for_each(lambda cls: (_sx_append(classes, cls) if sx_truthy((not sx_truthy(contains_p(classes, cls)))) else NIL), scan_css_classes(page_source)), classes))([]))(components_needed(page_source, env))
 
+# scan-io-refs-walk
+scan_io_refs_walk = lambda node, io_names, refs: ((lambda name: ((_sx_append(refs, name) if sx_truthy((not sx_truthy(contains_p(refs, name)))) else NIL) if sx_truthy(contains_p(io_names, name)) else NIL))(symbol_name(node)) if sx_truthy((type_of(node) == 'symbol')) else (for_each(lambda item: scan_io_refs_walk(item, io_names, refs), node) if sx_truthy((type_of(node) == 'list')) else (for_each(lambda key: scan_io_refs_walk(dict_get(node, key), io_names, refs), keys(node)) if sx_truthy((type_of(node) == 'dict')) else NIL)))
+
+# scan-io-refs
+scan_io_refs = lambda node, io_names: (lambda refs: _sx_begin(scan_io_refs_walk(node, io_names, refs), refs))([])
+
+# transitive-io-refs-walk
+transitive_io_refs_walk = lambda n, seen, all_refs, env, io_names: (_sx_begin(_sx_append(seen, n), (lambda val: (_sx_begin(for_each(lambda ref: (_sx_append(all_refs, ref) if sx_truthy((not sx_truthy(contains_p(all_refs, ref)))) else NIL), scan_io_refs(component_body(val), io_names)), for_each(lambda dep: transitive_io_refs_walk(dep, seen, all_refs, env, io_names), scan_refs(component_body(val)))) if sx_truthy((type_of(val) == 'component')) else (_sx_begin(for_each(lambda ref: (_sx_append(all_refs, ref) if sx_truthy((not sx_truthy(contains_p(all_refs, ref)))) else NIL), scan_io_refs(macro_body(val), io_names)), for_each(lambda dep: transitive_io_refs_walk(dep, seen, all_refs, env, io_names), scan_refs(macro_body(val)))) if sx_truthy((type_of(val) == 'macro')) else NIL)))(env_get(env, n))) if sx_truthy((not sx_truthy(contains_p(seen, n)))) else NIL)
+
+# transitive-io-refs
+transitive_io_refs = lambda name, env, io_names: (lambda all_refs: (lambda seen: (lambda key: _sx_begin(transitive_io_refs_walk(key, seen, all_refs, env, io_names), all_refs))((name if sx_truthy(starts_with_p(name, '~')) else sx_str('~', name))))([]))([])
+
+# compute-all-io-refs
+compute_all_io_refs = lambda env, io_names: for_each(lambda name: (lambda val: (component_set_io_refs(val, transitive_io_refs(name, env, io_names)) if sx_truthy((type_of(val) == 'component')) else NIL))(env_get(env, name)), env_components(env))
+
+# component-pure?
+component_pure_p = lambda name, env, io_names: empty_p(transitive_io_refs(name, env, io_names))
+
 
 # =========================================================================
 # Fixups -- wire up render adapter dispatch
diff --git a/shared/sx/types.py b/shared/sx/types.py
index 4207421..380f2ce 100644
--- a/shared/sx/types.py
+++ b/shared/sx/types.py
@@ -168,6 +168,12 @@ class Component:
     closure: dict[str, Any] = field(default_factory=dict)
     css_classes: set[str] = field(default_factory=set)  # pre-scanned :class values
     deps: set[str] = field(default_factory=set)        # transitive component deps (~names)
+    io_refs: set[str] = field(default_factory=set)     # transitive IO primitive refs
+
+    @property
+    def is_pure(self) -> bool:
+        """True if this component has no transitive IO dependencies."""
+        return not self.io_refs
 
     def __repr__(self):
         return f"<Component ~{self.name}({', '.join(self.params)})>"
diff --git a/sx/sx/analyzer.sx b/sx/sx/analyzer.sx
index 2220d76..43853f8 100644
--- a/sx/sx/analyzer.sx
+++ b/sx/sx/analyzer.sx
@@ -1,25 +1,30 @@
-;; Bundle analyzer — live demonstration of Phase 1 component dependency analysis.
+;; Bundle analyzer — live demonstration of dependency analysis + IO detection.
 ;; Shows per-page component bundles vs total, visualizing payload savings.
-;; @css bg-green-100 text-green-800 bg-violet-600 bg-stone-200 text-violet-600 text-stone-600 text-green-600 rounded-full h-2.5 grid-cols-3
+;; Phase 2 adds IO classification: which components are pure vs IO-dependent.
+;; @css bg-green-100 text-green-800 bg-violet-600 bg-stone-200 text-violet-600 text-stone-600 text-green-600 rounded-full h-2.5 grid-cols-3 bg-blue-100 text-blue-800 bg-amber-100 text-amber-800 grid-cols-4
 
-(defcomp ~bundle-analyzer-content (&key pages total-components total-macros)
+(defcomp ~bundle-analyzer-content (&key pages total-components total-macros
+                                        pure-count io-count)
   (~doc-page :title "Page Bundle Analyzer"
 
     (p :class "text-stone-600 mb-6"
-      "Live analysis of component dependency graphs across all pages in this app. "
+      "Live analysis of component dependency graphs and IO classification across all pages. "
       "Each bar shows how many of the "
       (strong (str total-components))
       " total components a page actually needs, computed by the "
       (a :href "/specs/deps" :class "text-violet-700 underline" "deps.sx")
-      " transitive closure algorithm.")
+      " transitive closure algorithm. "
+      "Phase 2 IO detection classifies each component as pure or IO-dependent.")
 
-    (div :class "mb-8 grid grid-cols-3 gap-4"
+    (div :class "mb-8 grid grid-cols-4 gap-4"
       (~analyzer-stat :label "Total Components" :value (str total-components)
                       :cls "text-violet-600")
       (~analyzer-stat :label "Total Macros" :value (str total-macros)
                       :cls "text-stone-600")
-      (~analyzer-stat :label "Pages Analyzed" :value (str (len pages))
-                      :cls "text-green-600"))
+      (~analyzer-stat :label "Pure Components" :value (str pure-count)
+                      :cls "text-blue-600")
+      (~analyzer-stat :label "IO-Dependent" :value (str io-count)
+                      :cls "text-amber-600"))
 
     (~doc-section :title "Per-Page Bundles" :id "bundles"
       (div :class "space-y-3"
@@ -31,7 +36,10 @@
             :direct (get page "direct")
             :total total-components
             :pct (get page "pct")
-            :savings (get page "savings")))
+            :savings (get page "savings")
+            :io-refs (get page "io-refs")
+            :pure-in-page (get page "pure-in-page")
+            :io-in-page (get page "io-in-page")))
           pages)))
 
     (~doc-section :title "How It Works" :id "how"
@@ -39,7 +47,8 @@
         (li (strong "Scan: ") "Regex finds all " (code "(~name") " patterns in the page's content expression.")
         (li (strong "Resolve: ") "Each referenced component's body AST is walked to find transitive " (code "~") " references.")
         (li (strong "Closure: ") "The full set is the union of direct + transitive deps, following chains through the component graph.")
-        (li (strong "Bundle: ") "Only these component definitions are serialized into the page payload. Everything else is omitted."))
+        (li (strong "Bundle: ") "Only these component definitions are serialized into the page payload. Everything else is omitted.")
+        (li (strong "IO detect: ") "Each component body is scanned for references to IO primitives (frag, query, service, etc.). Components with zero transitive IO refs are pure — safe for client rendering."))
       (p :class "mt-4 text-stone-600"
         "The analysis handles circular references (via seen-set), "
         "walks all branches of control flow (if/when/cond/case), "
@@ -50,18 +59,24 @@
     (div :class (str "text-3xl font-bold " cls) value)
     (div :class "text-sm text-stone-500 mt-1" label)))
 
-(defcomp ~analyzer-row (&key name path needed direct total pct savings)
+(defcomp ~analyzer-row (&key name path needed direct total pct savings
+                             io-refs pure-in-page io-in-page)
   (div :class "rounded border border-stone-200 p-4"
     (div :class "flex items-center justify-between mb-2"
       (div
         (span :class "font-mono font-semibold text-stone-800" name)
         (span :class "text-stone-400 text-sm ml-2" path))
-      (div :class "text-right"
-        (span :class "font-mono text-sm"
-          (span :class "text-violet-700 font-bold" (str needed))
-          (span :class "text-stone-400" (str " / " total)))
-        (span :class "ml-2 inline-block px-1.5 py-0.5 rounded text-xs font-medium bg-green-100 text-green-800"
-          (str savings "% saved"))))
+      (div :class "flex items-center gap-2"
+        (span :class "inline-block px-1.5 py-0.5 rounded text-xs font-medium bg-blue-100 text-blue-800"
+          (str pure-in-page " pure"))
+        (span :class "inline-block px-1.5 py-0.5 rounded text-xs font-medium bg-amber-100 text-amber-800"
+          (str io-in-page " IO"))
+        (div :class "text-right"
+          (span :class "font-mono text-sm"
+            (span :class "text-violet-700 font-bold" (str needed))
+            (span :class "text-stone-400" (str " / " total)))
+          (span :class "ml-2 inline-block px-1.5 py-0.5 rounded text-xs font-medium bg-green-100 text-green-800"
+            (str savings "% saved")))))
     (div :class "w-full bg-stone-200 rounded-full h-2.5"
       (div :class "bg-violet-600 h-2.5 rounded-full transition-all"
            :style (str "width: " pct "%")))))
diff --git a/sx/sx/plans.sx b/sx/sx/plans.sx
index 5212469..c96617c 100644
--- a/sx/sx/plans.sx
+++ b/sx/sx/plans.sx
@@ -683,43 +683,61 @@
     ;; Phase 2
     ;; -----------------------------------------------------------------------
 
-    (~doc-section :title "Phase 2: Smart Server/Client Boundary" :id "phase-2"
+    (~doc-section :title "Phase 2: Smart Server/Client Boundary — IO Detection" :id "phase-2"
 
-      (div :class "rounded border border-violet-200 bg-violet-50 p-4 mb-4"
-        (p :class "text-violet-900 font-medium" "What it enables")
-        (p :class "text-violet-800" "Formalized partial evaluation model. Server evaluates IO, serializes pure subtrees. The system automatically knows \"this component needs server data\" vs \"this component is pure and can render anywhere.\""))
+      (div :class "rounded border border-green-300 bg-green-50 p-4 mb-4"
+        (div :class "flex items-center gap-2 mb-2"
+          (span :class "inline-block px-2 py-0.5 rounded text-xs font-bold bg-green-600 text-white uppercase" "Complete")
+          (a :href "/specs/deps" :class "text-green-700 underline text-sm font-medium" "View canonical spec: deps.sx")
+          (a :href "/isomorphism/bundle-analyzer" :class "text-green-700 underline text-sm font-medium" "Live bundle analyzer with IO"))
+        (p :class "text-green-900 font-medium" "What it enables")
+        (p :class "text-green-800" "Automatic IO detection and selective expansion. Server expands IO-dependent components, serializes pure ones for client. Per-component intelligence replaces global toggle."))
 
-      (~doc-subsection :title "Current Mechanism"
-        (p "_aser in async_eval.py already does partial evaluation — IO primitives are awaited and substituted, HTML tags and component calls serialize as SX. The _expand_components context var controls expansion. But this is a global toggle, not per-component."))
-
-      (~doc-subsection :title "Approach"
+      (~doc-subsection :title "IO Detection in the Spec"
+        (p "Five new functions in "
+          (a :href "/specs/deps" :class "text-violet-700 underline" "deps.sx")
+          " extend the Phase 1 walker to detect IO primitive references:")
 
         (div :class "space-y-4"
           (div
-            (h4 :class "font-semibold text-stone-700" "1. Automatic IO detection")
-            (p "Extend Phase 1 AST walker to check for references to IO_PRIMITIVES names (frag, query, service, current-user, etc.).")
-            (~doc-code :code (highlight "def has_io_deps(name: str, env: dict) -> bool:\n    \"\"\"True if component transitively references any IO primitive.\"\"\"\n    ..." "python")))
+            (h4 :class "font-semibold text-stone-700" "1. IO scanning")
+            (p (code "scan-io-refs") " walks an AST node, collecting symbol names that match an IO name set. The IO set is provided by the host from boundary declarations (all three tiers: core IO, deployment IO, page helpers).")
+            (~doc-code :code (highlight "(define scan-io-refs\n  (fn (node io-names)\n    (let ((refs (list)))\n      (scan-io-refs-walk node io-names refs)\n      refs)))" "lisp")))
 
           (div
-            (h4 :class "font-semibold text-stone-700" "2. Component metadata")
-            (~doc-code :code (highlight "ComponentMeta:\n  deps: set[str]        # transitive component deps (Phase 1)\n  io_refs: set[str]     # IO primitive names referenced\n  is_pure: bool         # True if io_refs empty (transitively)" "python")))
+            (h4 :class "font-semibold text-stone-700" "2. Transitive IO closure")
+            (p (code "transitive-io-refs") " follows component deps recursively, unioning IO refs from all reachable components and macros. Cycle-safe via seen-set.")
+            (~doc-code :code (highlight "(define transitive-io-refs\n  (fn (name env io-names)\n    ;; Walk deps, scan each body for IO refs,\n    ;; union all refs transitively.\n    ...))" "lisp")))
 
           (div
-            (h4 :class "font-semibold text-stone-700" "3. Selective expansion")
-            (p "Refine _aser: instead of checking a global _expand_components flag, check the component's is_pure metadata:")
-            (ul :class "list-disc pl-5 text-stone-700 space-y-1"
-              (li "IO-dependent → expand server-side (IO must resolve)")
-              (li "Pure → serialize for client (let client render)")
-              (li "Explicit override: :server true on defcomp forces server expansion")))
+            (h4 :class "font-semibold text-stone-700" "3. Batch computation")
+            (p (code "compute-all-io-refs") " iterates the env, computes transitive IO refs for each component, and caches the result via " (code "component-set-io-refs!") ". Called after " (code "compute-all-deps") " at component registration time."))
 
           (div
-            (h4 :class "font-semibold text-stone-700" "4. Data manifest for pages")
-            (p "PageDef produces a declaration of what IO the page needs, enabling Phase 3 (client can prefetch data) and Phase 5 (streaming)."))))
+            (h4 :class "font-semibold text-stone-700" "4. Component metadata")
+            (p "Each component now carries " (code "io_refs") " (transitive IO primitive names) alongside " (code "deps") " and " (code "css_classes") ". The derived " (code "is_pure") " property is true when " (code "io_refs") " is empty — the component can render anywhere without server data."))))
+
+      (~doc-subsection :title "Selective Expansion"
+        (p "The partial evaluator " (code "_aser") " now uses per-component IO metadata instead of a global toggle:")
+        (ul :class "list-disc pl-5 text-stone-700 space-y-1"
+          (li (strong "IO-dependent") " → expand server-side (IO must resolve)")
+          (li (strong "Pure") " → serialize for client (let client render)")
+          (li (strong "Layout slot context") " → all components still expand (backwards compat via " (code "_expand_components") " context var)"))
+        (p "A component calling " (code "(highlight ...)") " or " (code "(query ...)") " is IO-dependent. A component with only HTML tags and string ops is pure."))
+
+      (~doc-subsection :title "Platform interface additions"
+        (p "Two new platform functions each host implements:")
+        (ul :class "list-disc pl-5 text-stone-700 space-y-1 font-mono text-sm"
+          (li "(component-io-refs c) → cached IO ref list")
+          (li "(component-set-io-refs! c refs) → cache IO refs on component")))
 
       (~doc-subsection :title "Verification"
         (ul :class "list-disc pl-5 text-stone-700 space-y-1"
-          (li "Components calling (query ...) classified IO-dependent; pure components classified pure")
-          (li "Existing pages produce identical output (regression)"))))
+          (li "Components calling (query ...) or (highlight ...) classified IO-dependent")
+          (li "Pure components (HTML-only) classified pure with empty io_refs")
+          (li "Transitive IO detection: component calling ~other where ~other calls (current-user) → IO-dependent")
+          (li "Bootstrapped to both hosts (sx_ref.py + sx-ref.js)")
+          (li (a :href "/isomorphism/bundle-analyzer" :class "text-violet-700 underline" "Live bundle analyzer") " shows per-page IO classification"))))
 
     ;; -----------------------------------------------------------------------
     ;; Phase 3
diff --git a/sx/sxc/pages/docs.sx b/sx/sxc/pages/docs.sx
index 944ea4b..21a71bd 100644
--- a/sx/sxc/pages/docs.sx
+++ b/sx/sxc/pages/docs.sx
@@ -414,7 +414,8 @@
     :selected (or (find-current isomorphism-nav-items slug) ""))
   :content (case slug
     "bundle-analyzer" (~bundle-analyzer-content
-      :pages pages :total-components total-components :total-macros total-macros)
+      :pages pages :total-components total-components :total-macros total-macros
+      :pure-count pure-count :io-count io-count)
     :else (~plan-isomorphic-content)))
 
 (defpage bundle-analyzer
@@ -428,7 +429,8 @@
     :selected "Bundle Analyzer")
   :data (bundle-analyzer-data)
   :content (~bundle-analyzer-content
-    :pages pages :total-components total-components :total-macros total-macros))
+    :pages pages :total-components total-components :total-macros total-macros
+    :pure-count pure-count :io-count io-count))
 
 ;; ---------------------------------------------------------------------------
 ;; Plans section
diff --git a/sx/sxc/pages/helpers.py b/sx/sxc/pages/helpers.py
index 709bb2a..03ff445 100644
--- a/sx/sxc/pages/helpers.py
+++ b/sx/sxc/pages/helpers.py
@@ -277,6 +277,8 @@ def _bundle_analyzer_data() -> dict:
     env = get_component_env()
     total_components = sum(1 for v in env.values() if isinstance(v, Component))
     total_macros = sum(1 for v in env.values() if isinstance(v, Macro))
+    pure_count = sum(1 for v in env.values() if isinstance(v, Component) and v.is_pure)
+    io_count = total_components - pure_count
 
     pages_data = []
     for name, page_def in sorted(get_all_pages("sx").items()):
@@ -286,6 +288,20 @@ def _bundle_analyzer_data() -> dict:
         n = len(needed)
         pct = round(n / total_components * 100) if total_components else 0
         savings = 100 - pct
+
+        # IO classification for components in this page
+        pure_in_page = 0
+        io_in_page = 0
+        page_io_refs: set[str] = set()
+        for comp_name in needed:
+            val = env.get(comp_name)
+            if isinstance(val, Component):
+                if val.is_pure:
+                    pure_in_page += 1
+                else:
+                    io_in_page += 1
+                    page_io_refs.update(val.io_refs)
+
         pages_data.append({
             "name": name,
             "path": page_def.path,
@@ -293,6 +309,9 @@ def _bundle_analyzer_data() -> dict:
             "needed": n,
             "pct": pct,
             "savings": savings,
+            "io-refs": len(page_io_refs),
+            "pure-in-page": pure_in_page,
+            "io-in-page": io_in_page,
         })
 
     pages_data.sort(key=lambda p: p["needed"], reverse=True)
@@ -301,6 +320,8 @@ def _bundle_analyzer_data() -> dict:
         "pages": pages_data,
         "total-components": total_components,
         "total-macros": total_macros,
+        "pure-count": pure_count,
+        "io-count": io_count,
     }