diff --git a/Makefile b/Makefile
index bd97eb45..36321ba5 100644
--- a/Makefile
+++ b/Makefile
@@ -329,6 +329,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_isas_spread_variant \
 	  $(BIN)/test_tagged_widen_named_variant \
 	  $(BIN)/test_io_vtable_run \
+	  $(BIN)/test_io_handle_run \
 	  $(BIN)/test_memio_vstream_run \
 	  $(BIN)/test_fmt_vstream_run \
 	  $(BIN)/test_fmt_vstream_mods_run \
@@ -707,6 +708,12 @@ $(BIN)/test_io_vtable_run: test/wcc/775_io_vtable_run.c \
 		$(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_io_handle_run: test/wcc/791_io_handle_run.c \
+		$(BIN)/ww $(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
+		$(BIN)/ww_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \
+		$(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 $(BIN)/test_memio_vstream_run: test/wcc/776_memio_vstream_run.c \
 		$(BIN)/ww $(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
 		$(BIN)/ww_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \
diff --git a/lib/io/stream.ww b/lib/io/stream.ww
index 5d63e0c7..f6f62b32 100644
--- a/lib/io/stream.ww
+++ b/lib/io/stream.ww
@@ -31,23 +31,31 @@
 
 package io;
 
+// Q2 layering (ratified): the file-arm of the handle dispatchers routes
+// to os.{read,write,close,lseek}; ww `os` plays Hare's `sys` role, so
+// `lib/io import os` is the correct direction (os is the import floor).
+import os;
+
 // ref/hare/io/stream.ha:36-42. Nullable spelling per #192 (ww parser
-// rejects `nullable *T`); each slot is `(*T | void)`.
+// rejects `nullable *T`); each slot is `(*T | void)`. The `seeker` slot
+// (4th) lands with io fold-2 (#5); `copier` stays deferred.
 export type vtable = struct {
 	reader: (*reader | void),
 	writer: (*writer | void),
 	closer: (*closer | void),
+	seeker: (*seeker | void),
 };
 
 // ref/hare/io/stream.ha:33.
 export type stream = *vtable;
 
-// ref/hare/io/stream.ha:44-50. The void-arm `return e;` chains two
+// ref/hare/io/stream.ha:44-51. Private stream-arm body behind the
+// handle-typed [[read]] (#5). The void-arm `return e;` chains two
 // direct widens: `errors.unsupported → error` via #199 α, then
 // `error → (size | eof | error)` via #205. The call-arm spells the
 // fn-ptr call explicitly per #193 (ww requires `(*r)(args)` rather
 // than implicit `r(args)`).
-export fn read(s: stream, buf: []u8) (size | eof | error) = {
+fn st_read(s: stream, buf: []u8) (size | eof | error) = {
 	match (s.reader) {
 	case void => {
 		let u: errors.unsupported;
@@ -58,8 +66,8 @@ export fn read(s: stream, buf: []u8) (size | eof | error) = {
 	};
 };
 
-// ref/hare/io/stream.ha:53-59.
-export fn write(s: stream, buf: []u8) (size | error) = {
+// ref/hare/io/stream.ha:53-60.
+fn st_write(s: stream, buf: []u8) (size | error) = {
 	match (s.writer) {
 	case void => {
 		let u: errors.unsupported;
@@ -74,9 +82,104 @@ export fn write(s: stream, buf: []u8) (size | error) = {
 // `c(s)?;` then falls through to the void arm; ww collapses to a
 // direct return for the void-arm fall-through shape. The surface
 // (void | error) matches.
-export fn close(s: stream) (void | error) = {
+fn st_close(s: stream) (void | error) = {
 	match (s.closer) {
 	case void => return void;
 	case let c: *closer => return (*c)(s);
 	};
 };
+
+// ref/hare/io/stream.ha:70-77. Clone of st_read's slot-dispatch shape
+// over the new `seeker` vtable slot.
+fn st_seek(s: stream, off: off, w: whence) (off | error) = {
+	match (s.seeker) {
+	case void => {
+		let u: errors.unsupported;
+		let e: error = u;
+		return e;
+	};
+	case let sk: *seeker => return (*sk)(s, off, w);
+	};
+};
+
+// ref/hare/io/handle.ha:16-23. The handle-typed public read: the
+// file-arm routes to os.read (Q2 layering), the stream-arm delegates to
+// the unchanged st_read vtable dispatch above.
+export fn read(h: handle, buf: []u8) (size | eof | error) = {
+	match (h) {
+	case let fd: file => {
+		let r: i64 = os.read(fd, buf.ptr, buf.len: u64);
+		if (r < 0) {
+			// #199b: faithful errno→io.error needs the ...errors.error spread; see lib/io/types.ww:40
+			let u: errors.unsupported;
+			let e: error = u;
+			return e;
+		};
+		if (r == 0) {
+			let z: eof;
+			return z;
+		};
+		return r: size;
+	};
+	case let s: stream => return st_read(s, buf);
+	};
+};
+
+// ref/hare/io/handle.ha:27-36.
+export fn write(h: handle, buf: []u8) (size | error) = {
+	match (h) {
+	case let fd: file => {
+		let r: i64 = os.write(fd, buf.ptr, buf.len: u64);
+		if (r < 0) {
+			// #199b: faithful errno→io.error needs the ...errors.error spread; see lib/io/types.ww:40
+			let u: errors.unsupported;
+			let e: error = u;
+			return e;
+		};
+		return r: size;
+	};
+	case let s: stream => return st_write(s, buf);
+	};
+};
+
+// ref/hare/io/handle.ha:44-51. Hare propagates each arm's error via `?`
+// then falls through; ww returns directly (matching st_close's shape).
+export fn close(h: handle) (void | error) = {
+	match (h) {
+	case let fd: file => {
+		let r: i32 = os.close(fd);
+		if (r < 0) {
+			// #199b: faithful errno→io.error needs the ...errors.error spread; see lib/io/types.ww:40
+			let u: errors.unsupported;
+			let e: error = u;
+			return e;
+		};
+		return void;
+	};
+	case let s: stream => return st_close(s);
+	};
+};
+
+// ref/hare/io/handle.ha:55-62. The io.whence → os.whence cast bridges
+// the two enum copies (same SET/CUR/END values); os.lseek owns the
+// syscall.
+export fn seek(h: handle, off: off, w: whence) (off | error) = {
+	match (h) {
+	case let fd: file => {
+		let r: i64 = os.lseek(fd, off, w: os.whence);
+		if (r < 0) {
+			// #199b: faithful errno→io.error needs the ...errors.error spread; see lib/io/types.ww:40
+			let u: errors.unsupported;
+			let e: error = u;
+			return e;
+		};
+		return r: off;
+	};
+	case let s: stream => return st_seek(s, off, w);
+	};
+};
+
+// ref/hare/io/handle.ha:65-67.
+export fn tell(h: handle) (off | error) = {
+	return seek(h, 0, whence.CUR);
+};
diff --git a/lib/io/types.ww b/lib/io/types.ww
index 7de7becc..c985bef1 100644
--- a/lib/io/types.ww
+++ b/lib/io/types.ww
@@ -37,6 +37,21 @@ export type whence = enum i32 {
 	END = 2,
 };
 
+// ref/hare/io/+linux/platform_file.ha:13. Hare's `file = int`; on
+// linux/x86_64 Hare's `int` is 32-bit, but ww's `int` is an 8B machine
+// word, so a literal `int` here would be width-wrong for a fd. i32 is
+// width-faithful to Hare's real fd width (USER-ruled 2026-05-31).
+export type file = i32;
+
+// ref/hare/io/arch+x86_64.ha:6. ABI-compatible with POSIX off_t.
+export type off = i64;
+
+// ref/hare/io/handle.ha:12. Hare spells it `(file | *stream)`; ww's
+// `stream` is already `*vtable` (the #94 collapse absorbed Hare's
+// `*stream` indirection), so the faithful ww payload is `(file |
+// stream)`, NOT a literal `*stream` which would be a double-pointer.
+export type handle = (file | stream);
+
 // ref/hare/io/types.ha:11 spreads `...errors::error` into the union;
 // ww enumerates the tags explicitly (ken's #204-block — spread of an
 // errors-side tagged into this union triggers a wrapper-vs-flatten
@@ -58,3 +73,8 @@ export type writer = fn(s: stream, buf: []u8) (size | error);
 
 // ref/hare/io/types.ha:55.
 export type closer = fn(s: stream) (void | error);
+
+// ref/hare/io/types.ha:76. Hare's `fn(s: *stream, off: off, w: whence)`;
+// ww's `stream` is already `*vtable` (the #94 collapse), so the param is
+// `stream` directly, mirroring the reader/writer/closer aliases above.
+export type seeker = fn(s: stream, off: off, w: whence) (off | error);
diff --git a/selfhost/cmd/w6c/main.combined.ww b/selfhost/cmd/w6c/main.combined.ww
index 86763636..514e19a9 100644
--- a/selfhost/cmd/w6c/main.combined.ww
+++ b/selfhost/cmd/w6c/main.combined.ww
@@ -14250,23 +14250,31 @@ export type underread = !i32;
 
 package io;
 
+// Q2 layering (ratified): the file-arm of the handle dispatchers routes
+// to os.{read,write,close,lseek}; ww `os` plays Hare's `sys` role, so
+// `lib/io import os` is the correct direction (os is the import floor).
+import os;
+
 // ref/hare/io/stream.ha:36-42. Nullable spelling per #192 (ww parser
-// rejects `nullable *T`); each slot is `(*T | void)`.
+// rejects `nullable *T`); each slot is `(*T | void)`. The `seeker` slot
+// (4th) lands with io fold-2 (#5); `copier` stays deferred.
 export type vtable = struct {
 	reader: (*reader | void),
 	writer: (*writer | void),
 	closer: (*closer | void),
+	seeker: (*seeker | void),
 };
 
 // ref/hare/io/stream.ha:33.
 export type stream = *vtable;
 
-// ref/hare/io/stream.ha:44-50. The void-arm `return e;` chains two
+// ref/hare/io/stream.ha:44-51. Private stream-arm body behind the
+// handle-typed [[read]] (#5). The void-arm `return e;` chains two
 // direct widens: `errors.unsupported → error` via #199 α, then
 // `error → (size | eof | error)` via #205. The call-arm spells the
 // fn-ptr call explicitly per #193 (ww requires `(*r)(args)` rather
 // than implicit `r(args)`).
-export fn read(s: stream, buf: []u8) (size | eof | error) = {
+fn st_read(s: stream, buf: []u8) (size | eof | error) = {
 	match (s.reader) {
 	case void => {
 		let u: errors.unsupported;
@@ -14277,8 +14285,8 @@ export fn read(s: stream, buf: []u8) (size | eof | error) = {
 	};
 };
 
-// ref/hare/io/stream.ha:53-59.
-export fn write(s: stream, buf: []u8) (size | error) = {
+// ref/hare/io/stream.ha:53-60.
+fn st_write(s: stream, buf: []u8) (size | error) = {
 	match (s.writer) {
 	case void => {
 		let u: errors.unsupported;
@@ -14293,13 +14301,108 @@ export fn write(s: stream, buf: []u8) (size | error) = {
 // `c(s)?;` then falls through to the void arm; ww collapses to a
 // direct return for the void-arm fall-through shape. The surface
 // (void | error) matches.
-export fn close(s: stream) (void | error) = {
+fn st_close(s: stream) (void | error) = {
 	match (s.closer) {
 	case void => return void;
 	case let c: *closer => return (*c)(s);
 	};
 };
 
+// ref/hare/io/stream.ha:70-77. Clone of st_read's slot-dispatch shape
+// over the new `seeker` vtable slot.
+fn st_seek(s: stream, off: off, w: whence) (off | error) = {
+	match (s.seeker) {
+	case void => {
+		let u: errors.unsupported;
+		let e: error = u;
+		return e;
+	};
+	case let sk: *seeker => return (*sk)(s, off, w);
+	};
+};
+
+// ref/hare/io/handle.ha:16-23. The handle-typed public read: the
+// file-arm routes to os.read (Q2 layering), the stream-arm delegates to
+// the unchanged st_read vtable dispatch above.
+export fn read(h: handle, buf: []u8) (size | eof | error) = {
+	match (h) {
+	case let fd: file => {
+		let r: i64 = os.read(fd, buf.ptr, buf.len: u64);
+		if (r < 0) {
+			// #199b: faithful errno→io.error needs the ...errors.error spread; see lib/io/types.ww:40
+			let u: errors.unsupported;
+			let e: error = u;
+			return e;
+		};
+		if (r == 0) {
+			let z: eof;
+			return z;
+		};
+		return r: size;
+	};
+	case let s: stream => return st_read(s, buf);
+	};
+};
+
+// ref/hare/io/handle.ha:27-36.
+export fn write(h: handle, buf: []u8) (size | error) = {
+	match (h) {
+	case let fd: file => {
+		let r: i64 = os.write(fd, buf.ptr, buf.len: u64);
+		if (r < 0) {
+			// #199b: faithful errno→io.error needs the ...errors.error spread; see lib/io/types.ww:40
+			let u: errors.unsupported;
+			let e: error = u;
+			return e;
+		};
+		return r: size;
+	};
+	case let s: stream => return st_write(s, buf);
+	};
+};
+
+// ref/hare/io/handle.ha:44-51. Hare propagates each arm's error via `?`
+// then falls through; ww returns directly (matching st_close's shape).
+export fn close(h: handle) (void | error) = {
+	match (h) {
+	case let fd: file => {
+		let r: i32 = os.close(fd);
+		if (r < 0) {
+			// #199b: faithful errno→io.error needs the ...errors.error spread; see lib/io/types.ww:40
+			let u: errors.unsupported;
+			let e: error = u;
+			return e;
+		};
+		return void;
+	};
+	case let s: stream => return st_close(s);
+	};
+};
+
+// ref/hare/io/handle.ha:55-62. The io.whence → os.whence cast bridges
+// the two enum copies (same SET/CUR/END values); os.lseek owns the
+// syscall.
+export fn seek(h: handle, off: off, w: whence) (off | error) = {
+	match (h) {
+	case let fd: file => {
+		let r: i64 = os.lseek(fd, off, w: os.whence);
+		if (r < 0) {
+			// #199b: faithful errno→io.error needs the ...errors.error spread; see lib/io/types.ww:40
+			let u: errors.unsupported;
+			let e: error = u;
+			return e;
+		};
+		return r: off;
+	};
+	case let s: stream => return st_seek(s, off, w);
+	};
+};
+
+// ref/hare/io/handle.ha:65-67.
+export fn tell(h: handle) (off | error) = {
+	return seek(h, 0, whence.CUR);
+};
+
 // errors — domain-agnostic error types. Mirrors ref/hare/errors/.
 //
 // Named-void tagged-union variants, so `(T | errors.invalid | ...)`
@@ -14475,6 +14578,21 @@ export type whence = enum i32 {
 	END = 2,
 };
 
+// ref/hare/io/+linux/platform_file.ha:13. Hare's `file = int`; on
+// linux/x86_64 Hare's `int` is 32-bit, but ww's `int` is an 8B machine
+// word, so a literal `int` here would be width-wrong for a fd. i32 is
+// width-faithful to Hare's real fd width (USER-ruled 2026-05-31).
+export type file = i32;
+
+// ref/hare/io/arch+x86_64.ha:6. ABI-compatible with POSIX off_t.
+export type off = i64;
+
+// ref/hare/io/handle.ha:12. Hare spells it `(file | *stream)`; ww's
+// `stream` is already `*vtable` (the #94 collapse absorbed Hare's
+// `*stream` indirection), so the faithful ww payload is `(file |
+// stream)`, NOT a literal `*stream` which would be a double-pointer.
+export type handle = (file | stream);
+
 // ref/hare/io/types.ha:11 spreads `...errors::error` into the union;
 // ww enumerates the tags explicitly (ken's #204-block — spread of an
 // errors-side tagged into this union triggers a wrapper-vs-flatten
@@ -14497,6 +14615,11 @@ export type writer = fn(s: stream, buf: []u8) (size | error);
 // ref/hare/io/types.ha:55.
 export type closer = fn(s: stream) (void | error);
 
+// ref/hare/io/types.ha:76. Hare's `fn(s: *stream, off: off, w: whence)`;
+// ww's `stream` is already `*vtable` (the #94 collapse), so the param is
+// `stream` directly, mirroring the reader/writer/closer aliases above.
+export type seeker = fn(s: stream, off: off, w: whence) (off | error);
+
 // memio — in-memory io stream. Project #94 fold-eFinal.
 //
 // Hare's memio:: surface, drop underscores. Two flavours behind a
diff --git a/selfhost/cmd/wwdump/main.combined.ww b/selfhost/cmd/wwdump/main.combined.ww
index 62d3d102..1f7257af 100644
--- a/selfhost/cmd/wwdump/main.combined.ww
+++ b/selfhost/cmd/wwdump/main.combined.ww
@@ -14250,23 +14250,31 @@ export type underread = !i32;
 
 package io;
 
+// Q2 layering (ratified): the file-arm of the handle dispatchers routes
+// to os.{read,write,close,lseek}; ww `os` plays Hare's `sys` role, so
+// `lib/io import os` is the correct direction (os is the import floor).
+import os;
+
 // ref/hare/io/stream.ha:36-42. Nullable spelling per #192 (ww parser
-// rejects `nullable *T`); each slot is `(*T | void)`.
+// rejects `nullable *T`); each slot is `(*T | void)`. The `seeker` slot
+// (4th) lands with io fold-2 (#5); `copier` stays deferred.
 export type vtable = struct {
 	reader: (*reader | void),
 	writer: (*writer | void),
 	closer: (*closer | void),
+	seeker: (*seeker | void),
 };
 
 // ref/hare/io/stream.ha:33.
 export type stream = *vtable;
 
-// ref/hare/io/stream.ha:44-50. The void-arm `return e;` chains two
+// ref/hare/io/stream.ha:44-51. Private stream-arm body behind the
+// handle-typed [[read]] (#5). The void-arm `return e;` chains two
 // direct widens: `errors.unsupported → error` via #199 α, then
 // `error → (size | eof | error)` via #205. The call-arm spells the
 // fn-ptr call explicitly per #193 (ww requires `(*r)(args)` rather
 // than implicit `r(args)`).
-export fn read(s: stream, buf: []u8) (size | eof | error) = {
+fn st_read(s: stream, buf: []u8) (size | eof | error) = {
 	match (s.reader) {
 	case void => {
 		let u: errors.unsupported;
@@ -14277,8 +14285,8 @@ export fn read(s: stream, buf: []u8) (size | eof | error) = {
 	};
 };
 
-// ref/hare/io/stream.ha:53-59.
-export fn write(s: stream, buf: []u8) (size | error) = {
+// ref/hare/io/stream.ha:53-60.
+fn st_write(s: stream, buf: []u8) (size | error) = {
 	match (s.writer) {
 	case void => {
 		let u: errors.unsupported;
@@ -14293,13 +14301,108 @@ export fn write(s: stream, buf: []u8) (size | error) = {
 // `c(s)?;` then falls through to the void arm; ww collapses to a
 // direct return for the void-arm fall-through shape. The surface
 // (void | error) matches.
-export fn close(s: stream) (void | error) = {
+fn st_close(s: stream) (void | error) = {
 	match (s.closer) {
 	case void => return void;
 	case let c: *closer => return (*c)(s);
 	};
 };
 
+// ref/hare/io/stream.ha:70-77. Clone of st_read's slot-dispatch shape
+// over the new `seeker` vtable slot.
+fn st_seek(s: stream, off: off, w: whence) (off | error) = {
+	match (s.seeker) {
+	case void => {
+		let u: errors.unsupported;
+		let e: error = u;
+		return e;
+	};
+	case let sk: *seeker => return (*sk)(s, off, w);
+	};
+};
+
+// ref/hare/io/handle.ha:16-23. The handle-typed public read: the
+// file-arm routes to os.read (Q2 layering), the stream-arm delegates to
+// the unchanged st_read vtable dispatch above.
+export fn read(h: handle, buf: []u8) (size | eof | error) = {
+	match (h) {
+	case let fd: file => {
+		let r: i64 = os.read(fd, buf.ptr, buf.len: u64);
+		if (r < 0) {
+			// #199b: faithful errno→io.error needs the ...errors.error spread; see lib/io/types.ww:40
+			let u: errors.unsupported;
+			let e: error = u;
+			return e;
+		};
+		if (r == 0) {
+			let z: eof;
+			return z;
+		};
+		return r: size;
+	};
+	case let s: stream => return st_read(s, buf);
+	};
+};
+
+// ref/hare/io/handle.ha:27-36.
+export fn write(h: handle, buf: []u8) (size | error) = {
+	match (h) {
+	case let fd: file => {
+		let r: i64 = os.write(fd, buf.ptr, buf.len: u64);
+		if (r < 0) {
+			// #199b: faithful errno→io.error needs the ...errors.error spread; see lib/io/types.ww:40
+			let u: errors.unsupported;
+			let e: error = u;
+			return e;
+		};
+		return r: size;
+	};
+	case let s: stream => return st_write(s, buf);
+	};
+};
+
+// ref/hare/io/handle.ha:44-51. Hare propagates each arm's error via `?`
+// then falls through; ww returns directly (matching st_close's shape).
+export fn close(h: handle) (void | error) = {
+	match (h) {
+	case let fd: file => {
+		let r: i32 = os.close(fd);
+		if (r < 0) {
+			// #199b: faithful errno→io.error needs the ...errors.error spread; see lib/io/types.ww:40
+			let u: errors.unsupported;
+			let e: error = u;
+			return e;
+		};
+		return void;
+	};
+	case let s: stream => return st_close(s);
+	};
+};
+
+// ref/hare/io/handle.ha:55-62. The io.whence → os.whence cast bridges
+// the two enum copies (same SET/CUR/END values); os.lseek owns the
+// syscall.
+export fn seek(h: handle, off: off, w: whence) (off | error) = {
+	match (h) {
+	case let fd: file => {
+		let r: i64 = os.lseek(fd, off, w: os.whence);
+		if (r < 0) {
+			// #199b: faithful errno→io.error needs the ...errors.error spread; see lib/io/types.ww:40
+			let u: errors.unsupported;
+			let e: error = u;
+			return e;
+		};
+		return r: off;
+	};
+	case let s: stream => return st_seek(s, off, w);
+	};
+};
+
+// ref/hare/io/handle.ha:65-67.
+export fn tell(h: handle) (off | error) = {
+	return seek(h, 0, whence.CUR);
+};
+
 // errors — domain-agnostic error types. Mirrors ref/hare/errors/.
 //
 // Named-void tagged-union variants, so `(T | errors.invalid | ...)`
@@ -14475,6 +14578,21 @@ export type whence = enum i32 {
 	END = 2,
 };
 
+// ref/hare/io/+linux/platform_file.ha:13. Hare's `file = int`; on
+// linux/x86_64 Hare's `int` is 32-bit, but ww's `int` is an 8B machine
+// word, so a literal `int` here would be width-wrong for a fd. i32 is
+// width-faithful to Hare's real fd width (USER-ruled 2026-05-31).
+export type file = i32;
+
+// ref/hare/io/arch+x86_64.ha:6. ABI-compatible with POSIX off_t.
+export type off = i64;
+
+// ref/hare/io/handle.ha:12. Hare spells it `(file | *stream)`; ww's
+// `stream` is already `*vtable` (the #94 collapse absorbed Hare's
+// `*stream` indirection), so the faithful ww payload is `(file |
+// stream)`, NOT a literal `*stream` which would be a double-pointer.
+export type handle = (file | stream);
+
 // ref/hare/io/types.ha:11 spreads `...errors::error` into the union;
 // ww enumerates the tags explicitly (ken's #204-block — spread of an
 // errors-side tagged into this union triggers a wrapper-vs-flatten
@@ -14497,6 +14615,11 @@ export type writer = fn(s: stream, buf: []u8) (size | error);
 // ref/hare/io/types.ha:55.
 export type closer = fn(s: stream) (void | error);
 
+// ref/hare/io/types.ha:76. Hare's `fn(s: *stream, off: off, w: whence)`;
+// ww's `stream` is already `*vtable` (the #94 collapse), so the param is
+// `stream` directly, mirroring the reader/writer/closer aliases above.
+export type seeker = fn(s: stream, off: off, w: whence) (off | error);
+
 // memio — in-memory io stream. Project #94 fold-eFinal.
 //
 // Hare's memio:: surface, drop underscores. Two flavours behind a
diff --git a/test/wcc/791_io_handle_run.c b/test/wcc/791_io_handle_run.c
new file mode 100644
index 00000000..b6584f7c
--- /dev/null
+++ b/test/wcc/791_io_handle_run.c
@@ -0,0 +1,378 @@
+/*
+ * 791_io_handle_run — project #5 commit-1 sentinel. Pins the lib/io
+ * handle dispatch surface: `handle = (file | stream)` and the
+ * read/write/close/seek/tell dispatchers (ref/hare/io/handle.ha:16-67)
+ * over BOTH arms:
+ *
+ *   - file-arm: a real OS fd (io.file = i32) routed to
+ *     os.{read,write,lseek,close} — the Q2 layering (lib/io imports os,
+ *     os is the import floor). The file-arm syscall-error path returns
+ *     the #199b errors.unsupported placeholder (see lib/io/types.ww:40),
+ *     pinned by the file_arm_error_stub row (a never-opened fd forces
+ *     EBADF on every file-arm dispatcher).
+ *   - stream-arm: a memio (or hand-built) vtable routed to the private
+ *     st_read/st_write/st_seek (ref/hare/io/stream.ha:44-77).
+ *
+ *   row                      | what it pins
+ *   -------------------------+--------------------------------------
+ *   file_arm_roundtrip       | open(/tmp) → io.write "ABC" → io.seek
+ *                            | SET 0 → io.read back → io.seek END == 3
+ *                            | → io.tell == 3 → io.close. Real fd
+ *                            | through every file-arm dispatcher;
+ *                            | SET+END+CUR(via tell) whence. exit 42.
+ *   stream_write_read        | memio.fixed: io.write 3 bytes, verify
+ *                            | the backing buffer, then read them back
+ *                            | through io.read on a fresh fixed stream.
+ *                            | exit 43.
+ *   stream_seek_unsupported  | memio wires no seeker slot; io.seek
+ *                            | takes st_seek's void-arm and returns an
+ *                            | io.error (not an off). exit 44.
+ *   stream_seeker_tell       | hand-built vtable WITH a seeker fn:
+ *                            | io.seek returns the seeker's off, and
+ *                            | io.tell == seek(s, 0, CUR). exit 45.
+ *   file_arm_error_stub      | never-opened fd (9999) → every file-arm
+ *                            | dispatcher's syscall returns -1 (EBADF)
+ *                            | → the #199b errors.unsupported stub
+ *                            | comes back as io.error. exit 46.
+ *
+ * Both stages run each row; cs.s == ww.s byte-id is asserted per row
+ * (rule-10). GATE POLARITY: must stay GREEN — a red means the handle
+ * union decompose, a dispatcher arm, or the seeker slot regressed.
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+
+static int
+runwait(const char *cmd)
+{
+	int rc = system(cmd);
+	if (rc == -1) return -1;
+	if (WIFEXITED(rc)) return WEXITSTATUS(rc);
+	return -1;
+}
+
+#define STAGE_CS	1
+#define STAGE_WW	2
+
+struct row {
+	const char *label;
+	const char *src;
+	int want_exit;
+	int stage_mask;
+	int byte_id;
+};
+
+static const struct row rows[] = {
+	{ "file_arm_roundtrip",
+	  "package main;\n"
+	  "import io;\n"
+	  "import os;\n"
+	  "export fn main() i32 = {\n"
+	  "    let cflags: os.flag = os.flag.RDWR | os.flag.CREATE | os.flag.TRUNC;\n"
+	  "    let fd: i32 = 0;\n"
+	  "    match (os.tryopen(\"/tmp/ww_io791_handle.dat\", cflags, 420i32)) {\n"
+	  "    case let e: os.oserror => return 81;\n"
+	  "    case let f: i32 => fd = f;\n"
+	  "    };\n"
+	  "    let h: io.file = fd;\n"
+	  "    let data: [3]u8;\n"
+	  "    data[0] = 65u8; data[1] = 66u8; data[2] = 67u8;\n"
+	  "    match (io.write(h, data[0:3])) {\n"
+	  "    case let n: size => { if (n != 3: size) { return 82; }; };\n"
+	  "    case let e: io.error => return 83;\n"
+	  "    };\n"
+	  "    match (io.seek(h, 0: io.off, io.whence.SET)) {\n"
+	  "    case let o: io.off => { if (o != 0: io.off) { return 84; }; };\n"
+	  "    case let e: io.error => return 85;\n"
+	  "    };\n"
+	  "    let rb: [3]u8;\n"
+	  "    match (io.read(h, rb[0:3])) {\n"
+	  "    case let n: size => { if (n != 3: size) { return 86; }; };\n"
+	  "    case let z: io.eof => return 87;\n"
+	  "    case let e: io.error => return 88;\n"
+	  "    };\n"
+	  "    if (rb[0] != 65u8 || rb[1] != 66u8 || rb[2] != 67u8) { return 89; };\n"
+	  "    match (io.seek(h, 0: io.off, io.whence.END)) {\n"
+	  "    case let o: io.off => { if (o != 3: io.off) { return 93; }; };\n"
+	  "    case let e: io.error => return 94;\n"
+	  "    };\n"
+	  "    match (io.tell(h)) {\n"
+	  "    case let o: io.off => { if (o != 3: io.off) { return 90; }; };\n"
+	  "    case let e: io.error => return 91;\n"
+	  "    };\n"
+	  "    match (io.close(h)) {\n"
+	  "    case void => void;\n"
+	  "    case let e: io.error => return 92;\n"
+	  "    };\n"
+	  "    return 42;\n"
+	  "};\n",
+	  42,
+	  STAGE_CS | STAGE_WW, 1 },
+	{ "stream_write_read",
+	  "package main;\n"
+	  "import io;\n"
+	  "import memio;\n"
+	  "export fn main() i32 = {\n"
+	  "    let buf: [8]u8;\n"
+	  "    let st: memio.stream = memio.fixed(buf[0:8]);\n"
+	  "    let s: io.stream = &st.vt;\n"
+	  "    let data: [3]u8;\n"
+	  "    data[0] = 88u8; data[1] = 89u8; data[2] = 90u8;\n"
+	  "    match (io.write(s, data[0:3])) {\n"
+	  "    case let n: size => { if (n != 3: size) { return 71; }; };\n"
+	  "    case let e: io.error => return 72;\n"
+	  "    };\n"
+	  "    if (buf[0] != 88u8 || buf[1] != 89u8 || buf[2] != 90u8) { return 73; };\n"
+	  "    let st2: memio.stream = memio.fixed(buf[0:8]);\n"
+	  "    let s2: io.stream = &st2.vt;\n"
+	  "    let rb: [3]u8;\n"
+	  "    match (io.read(s2, rb[0:3])) {\n"
+	  "    case let n: size => { if (n != 3: size) { return 74; }; };\n"
+	  "    case let z: io.eof => return 75;\n"
+	  "    case let e: io.error => return 76;\n"
+	  "    };\n"
+	  "    if (rb[0] != 88u8 || rb[1] != 89u8 || rb[2] != 90u8) { return 77; };\n"
+	  "    return 43;\n"
+	  "};\n",
+	  43,
+	  STAGE_CS | STAGE_WW, 1 },
+	{ "stream_seek_unsupported",
+	  "package main;\n"
+	  "import io;\n"
+	  "import memio;\n"
+	  "export fn main() i32 = {\n"
+	  "    let buf: [4]u8;\n"
+	  "    let st: memio.stream = memio.fixed(buf[0:4]);\n"
+	  "    let s: io.stream = &st.vt;\n"
+	  "    match (io.seek(s, 0: io.off, io.whence.SET)) {\n"
+	  "    case let o: io.off => return 61;\n"
+	  "    case let e: io.error => return 44;\n"
+	  "    };\n"
+	  "};\n",
+	  44,
+	  STAGE_CS | STAGE_WW, 1 },
+	{ "stream_seeker_tell",
+	  "package main;\n"
+	  "import io;\n"
+	  "fn myseek(s: io.stream, off: io.off, w: io.whence) (io.off | io.error) = {\n"
+	  "    return off + 100: io.off;\n"
+	  "};\n"
+	  "export fn main() i32 = {\n"
+	  "    let vt: io.vtable;\n"
+	  "    vt.seeker = (&myseek): *io.seeker;\n"
+	  "    let s: io.stream = &vt;\n"
+	  "    match (io.seek(s, 5: io.off, io.whence.SET)) {\n"
+	  "    case let o: io.off => { if (o != 105: io.off) { return 51; }; };\n"
+	  "    case let e: io.error => return 52;\n"
+	  "    };\n"
+	  "    match (io.tell(s)) {\n"
+	  "    case let o: io.off => { if (o != 100: io.off) { return 53; }; };\n"
+	  "    case let e: io.error => return 54;\n"
+	  "    };\n"
+	  "    return 45;\n"
+	  "};\n",
+	  45,
+	  STAGE_CS | STAGE_WW, 1 },
+	{ "file_arm_error_stub",
+	  "package main;\n"
+	  "import io;\n"
+	  "export fn main() i32 = {\n"
+	  /* A never-opened fd: every file-arm syscall returns -1 (EBADF),
+	   * driving the #199b errors.unsupported stub on all four
+	   * dispatchers (write/read/seek/close). Since that stub is the
+	   * only error-producing path reachable here, an io.error arm
+	   * taken == the placeholder came back. */
+	  "    let h: io.file = 9999i32;\n"
+	  "    let data: [3]u8;\n"
+	  "    data[0] = 65u8; data[1] = 66u8; data[2] = 67u8;\n"
+	  "    match (io.write(h, data[0:3])) {\n"
+	  "    case let n: size => return 61;\n"
+	  "    case let e: io.error => void;\n"
+	  "    };\n"
+	  "    match (io.read(h, data[0:3])) {\n"
+	  "    case let n: size => return 62;\n"
+	  "    case let z: io.eof => return 63;\n"
+	  "    case let e: io.error => void;\n"
+	  "    };\n"
+	  "    match (io.seek(h, 0: io.off, io.whence.SET)) {\n"
+	  "    case let o: io.off => return 64;\n"
+	  "    case let e: io.error => void;\n"
+	  "    };\n"
+	  "    match (io.close(h)) {\n"
+	  "    case void => return 65;\n"
+	  "    case let e: io.error => void;\n"
+	  "    };\n"
+	  "    return 46;\n"
+	  "};\n",
+	  46,
+	  STAGE_CS | STAGE_WW, 1 },
+};
+
+static int
+write_source(const char *path, const char *src)
+{
+	FILE *f = fopen(path, "wb");
+	if (!f) return -1;
+	fputs(src, f);
+	fclose(f);
+	return 0;
+}
+
+/* Per-row tmpdir cleanup. ww_ww writes intermediates next to the source
+ * (filed task #15), so each row's build leaves <src>.{combined.ww,s,o}
+ * + bare exe alongside. Sweep them all then rmdir. */
+static void
+cleanup_tmp(const char *tmpdir, const char *base)
+{
+	char p[640];
+	snprintf(p, sizeof p, "%s/%s.ww", tmpdir, base); unlink(p);
+	snprintf(p, sizeof p, "%s/%s.s",  tmpdir, base); unlink(p);
+	snprintf(p, sizeof p, "%s/%s.o",  tmpdir, base); unlink(p);
+	snprintf(p, sizeof p, "%s/%s.combined.ww", tmpdir, base); unlink(p);
+	snprintf(p, sizeof p, "%s/%s",    tmpdir, base); unlink(p);
+	rmdir(tmpdir);
+}
+
+static int
+build_via_driver(const char *driver, const char *tmpdir, const char *cwd,
+    const char *src)
+{
+	char cmd[2048];
+	snprintf(cmd, sizeof cmd,
+	    "cd %s && timeout 180 %s build -I %s/lib %s 2>/dev/null",
+	    tmpdir, driver, cwd, src);
+	return runwait(cmd);
+}
+
+static int
+run_row(const char *driver, const char *cwd, const struct row *r, int seq)
+{
+	char tmpdir[256], src[512], base[64], outbin[768];
+	snprintf(tmpdir, sizeof tmpdir, "/tmp/ioh_%d_d_%d", getpid(), seq);
+	snprintf(base,   sizeof base,   "main791");
+	snprintf(src,    sizeof src,    "%s/%s.ww", tmpdir, base);
+	mkdir(tmpdir, 0755);
+	if (write_source(src, r->src) != 0) { cleanup_tmp(tmpdir, base); return -1; }
+	int rc;
+	int br = build_via_driver(driver, tmpdir, cwd, src);
+	if (br == 0) {
+		snprintf(outbin, sizeof outbin, "%s/%s", tmpdir, base);
+		rc = runwait(outbin);
+	} else {
+		rc = -1;
+	}
+	cleanup_tmp(tmpdir, base);
+	return rc;
+}
+
+/* asm_byte_identical — diff cstage vs wwstage .s. Parallel trees so
+ * ww_ww writing intermediates next to the source doesn't clobber the
+ * cstage .s (CLAUDE.md rule 14 phase split). */
+static int
+asm_byte_identical(const char *cdrv, const char *wdrv, const char *cwd,
+    const struct row *r, int seq)
+{
+	char src[512], tdc[256], tdw[256], base[64], cs[512], ws[512];
+	snprintf(tdc, sizeof tdc, "/tmp/ioh_%d_c_%d", getpid(), seq);
+	snprintf(tdw, sizeof tdw, "/tmp/ioh_%d_w_%d", getpid(), seq);
+	snprintf(base, sizeof base, "main791");
+	mkdir(tdc, 0755);
+	mkdir(tdw, 0755);
+	snprintf(src, sizeof src, "%s/%s.ww", tdc, base);
+	if (write_source(src, r->src) != 0) { cleanup_tmp(tdc, base); cleanup_tmp(tdw, base); return -1; }
+	int rc = -1;
+	if (build_via_driver(cdrv, tdc, cwd, src) != 0) goto out;
+	snprintf(cs, sizeof cs, "%s/%s.s", tdc, base);
+
+	snprintf(src, sizeof src, "%s/%s.ww", tdw, base);
+	if (write_source(src, r->src) != 0) goto out;
+	if (build_via_driver(wdrv, tdw, cwd, src) != 0) goto out;
+	snprintf(ws, sizeof ws, "%s/%s.s", tdw, base);
+
+	FILE *fc = fopen(cs, "rb");
+	FILE *fw = fopen(ws, "rb");
+	if (fc && fw) {
+		rc = 0;
+		for (;;) {
+			int a = fgetc(fc);
+			int b = fgetc(fw);
+			if (a != b) { rc = -1; break; }
+			if (a == EOF) break;
+		}
+	}
+	if (fc) fclose(fc);
+	if (fw) fclose(fw);
+out:
+	cleanup_tmp(tdc, base);
+	cleanup_tmp(tdw, base);
+	return rc;
+}
+
+int
+main(void)
+{
+	const char *bin = getenv("BIN");
+	if (!bin) bin = "out/bin";
+	char cwd[256];
+	if (getcwd(cwd, sizeof cwd) == NULL) return 1;
+	char absbin[512];
+	if (bin[0] != '/') {
+		snprintf(absbin, sizeof absbin, "%s/%s", cwd, bin);
+		bin = absbin;
+	}
+
+	char cdrv[640], wdrv[640];
+	snprintf(cdrv, sizeof cdrv, "%s/ww",    bin);
+	snprintf(wdrv, sizeof wdrv, "%s/ww_ww", bin);
+
+	int n = (int)(sizeof rows / sizeof rows[0]);
+	int total = 0, fail = 0;
+	int wwpresent = (access(wdrv, X_OK) == 0);
+	int seq = 0;
+
+	for (int i = 0; i < n; i++) {
+		if (rows[i].stage_mask & STAGE_CS) {
+			total++;
+			int got = run_row(cdrv, cwd, &rows[i], seq++);
+			if (got != rows[i].want_exit) {
+				fprintf(stderr,
+				    "io_handle_run[cs][%s]: exit=%d want=%d\n",
+				    rows[i].label, got, rows[i].want_exit);
+				fail++;
+			}
+		}
+		if (wwpresent && (rows[i].stage_mask & STAGE_WW)) {
+			total++;
+			int got = run_row(wdrv, cwd, &rows[i], seq++);
+			if (got != rows[i].want_exit) {
+				fprintf(stderr,
+				    "io_handle_run[ww][%s]: exit=%d want=%d\n",
+				    rows[i].label, got, rows[i].want_exit);
+				fail++;
+			}
+			if (rows[i].byte_id) {
+				total++;
+				if (asm_byte_identical(cdrv, wdrv, cwd, &rows[i], seq++) != 0) {
+					fprintf(stderr,
+					    "io_handle_run[byte-id][%s]: cstage vs wwstage asm differs\n",
+					    rows[i].label);
+					fail++;
+				}
+			}
+		}
+	}
+
+	if (!wwpresent)
+		fprintf(stderr, "io_handle_run: skip wwstage (no %s)\n", wdrv);
+
+	if (fail) {
+		fprintf(stderr, "io_handle_run: %d/%d fixtures failed\n",
+		    fail, total);
+		return 1;
+	}
+	printf("io_handle_run: %d/%d ok\n", total, total);
+	return 0;
+}