p2: digest with in-sift FIFO, SQLite caches, Honcho context, recover

Dixie is capped (max_inflight 2, queue_depth 8, queue_wait 20s) and
never queued on llama-server. Streaming chat, thinking off, 45s
fallback to clean. Digest and chunk-embedding caches are
content-addressed SQLite (Honcho context is not cached). Recover
uses the guarded Fetcher. guardian-star is refused in code.

vendor/github.com/mattn/go-isatty/isatty_tiocgwinsz.go

@@ -0,0 +1,24 @@
+//go:build (linux || aix || zos) && !appengine && !tinygo
+// +build linux aix zos
+// +build !appengine
+// +build !tinygo
+
+package isatty
+
+import "golang.org/x/sys/unix"
+
+// IsTerminal return true if the file descriptor is terminal.
+// TIOCGWINSZ is used instead of TCGETS because TCGETS shares its ioctl
+// number with SNDCTL_TMR_TIMEBASE of the OSS sound API, so it may succeed
+// (and even change the device mode) on non-tty devices. musl's isatty does
+// the same.
+func IsTerminal(fd uintptr) bool {
+	_, err := unix.IoctlGetWinsize(int(fd), unix.TIOCGWINSZ)
+	return err == nil
+}
+
+// IsCygwinTerminal return true if the file descriptor is a cygwin or msys2
+// terminal. This is also always false on this environment.
+func IsCygwinTerminal(fd uintptr) bool {
+	return false
+}