Stop mislabeling truncated captures as "exact"

internal/proxy/tee.go's teeConn silently drops bytes past
maxCaptureBytes (10 MiB) but callers unconditionally marked the result
"exact" anyway. Confirmed live: proxying a 15 MiB response worked
correctly end-to-end (the client got the full, real 15 MiB - proxying
itself is unbounded, only storage is capped), but the stored history
entry was exactly 10485760 bytes with response_exact=1 still set. For a
tool whose core value proposition is "raw bytes are the source of
truth," a silently truncated capture presented as complete could hide
the very evidence a smuggling or parser-differential investigation is
looking for in the tail of a large body - and give false confidence
that it isn't there.

teeConn.Take() now returns (data, truncated) instead of just data;
truncated is true whenever a Read had to drop bytes because the buffer
was already at cap. Every caller (proxy.go's forward() on both the
request and response side, repeat.go's sendRaw for Repeater/Intruder)
now folds truncated into exact - a truncated capture is never marked
exact - and additionally threads a distinct RequestTruncated/
ResponseTruncated bool through store.Entry, ipc.EntryDetail, and the
TUI, since "truncated" and "reconstructed" (HTTP/2, which never had
wire-exact bytes to begin with) are different situations worth telling
apart: a truncated capture is still real wire bytes, just incomplete,
not a synthesized reconstruction. The detail/repeater views now show
"truncated (hit capture size limit)" specifically rather than lumping
it in with "reconstructed", which would have implied more
transformation happened than actually did.

Schema: history gains request_truncated/response_truncated columns via
the same ALTER-TABLE-and-ignore-duplicate-column pattern already used
for source/flagged, so existing databases upgrade in place.

Verified live: a target server returning a 15 MiB body (over the 10 MiB
cap) proxied through cleanly - full body reached the client - while the
stored entry shows length=10485760, response_exact=0,
response_truncated=1 (previously would have shown response_exact=1);
the TUI's Detail view correctly displays "Response (10485760 bytes,
truncated (hit capture size limit))" instead of "exact".

go build/vet/gofmt/test/mod tidy all clean.

1 files changed, 21 insertions, 8 deletions

diff --git a/internal/proxy/tee.go b/internal/proxy/tee.go
index f6a385a..bd34d19 100644
--- a/internal/proxy/tee.go
+++ b/internal/proxy/tee.go
@@ -22,8 +22,9 @@ const maxCaptureBytes = 10 << 20 // 10 MiB
 // here (call sites synchronize on the request/response boundary itself).
 type teeConn struct {
 	net.Conn
-	mu  sync.Mutex
-	buf []byte
+	mu        sync.Mutex
+	buf       []byte
+	truncated bool
 }
 
 func newTeeConn(c net.Conn) *teeConn {
@@ -34,12 +35,18 @@ func (c *teeConn) Read(p []byte) (int, error) {
 	n, err := c.Conn.Read(p)
 	if n > 0 {
 		c.mu.Lock()
-		if room := maxCaptureBytes - len(c.buf); room > 0 {
+		room := maxCaptureBytes - len(c.buf)
+		if room > 0 {
 			end := n
 			if end > room {
 				end = room
 			}
 			c.buf = append(c.buf, p[:end]...)
+			if end < n {
+				c.truncated = true
+			}
+		} else {
+			c.truncated = true
 		}
 		c.mu.Unlock()
 	}
@@ -47,13 +54,19 @@ func (c *teeConn) Read(p []byte) (int, error) {
 }
 
 // Take returns the bytes read since the last Take call (or since the
-// connection was created) and resets the buffer.
-func (c *teeConn) Take() []byte {
+// connection was created), whether that capture hit maxCaptureBytes and
+// had to drop bytes off the end, and resets both. A caller storing this
+// as an "exact" capture must fold truncated into that decision - bytes
+// silently missing from the tail is exactly the kind of gap "exact"
+// promises doesn't exist, and callers finding it separately or not at
+// all is how a request smuggling investigation loses the one thing it
+// was looking for.
+func (c *teeConn) Take() (data []byte, truncated bool) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
-	out := c.buf
-	c.buf = nil
-	return out
+	out, trunc := c.buf, c.truncated
+	c.buf, c.truncated = nil, false
+	return out, trunc
 }
 
 // teeListener wraps a net.Listener so every accepted connection is