9agents: /active/<h>/<pid>/chat, the conversation as one file per messageHEADmain

Each message of a claude or codex agent's transcript is a file named
<id>-<kind>: the id is its position in the transcript from 0, as 8
digits so the names sort; the kind is user, assistant, thinking, system
or agent, and a tool call is named after its tool (00000002-bash) and
its result after the call (00000003-bash-result). A file is the message
as text (a tool call: its name, then its input); its mtime is when it
was said.

chat.zig indexes a transcript incrementally, keyed by (dev, ino) and
checked by birth time and a hash of its first and last indexed bytes, so
a file rewritten in place is indexed again. It holds offsets, never
bytes: every read reads the file, and a read resumes where the last one
stopped so a long message is not decoded from its start each time. The
indexes and the runner live in lazily backed mappings (NORESERVE,
NOHUGEPAGE), and the fid table is 32768 so a kernel mount can hold every
message of a long chat.

A 9agents started inside a user namespace (from a 9ns-wrapped terminal)
cannot read /proc/<pid>/fd of processes outside it, so the fd route
never resolved codex there; /active now also finds a codex session
through the thread writer locks it holds (/proc/locks), via = lock.

Fixes to /active found on the way: a fifo in place of a transcript or
record no longer blocks the daemon; a transcript is opened from its
pinned root a component at a time, so a symlinked directory or a
sessionId with .. cannot reach outside it; slot generations are 24 bits,
so a stale node id cannot come to name another agent; listing a harness
rescans; an agent that had not resolved yet is asked again.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

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