docs: four directories, and a rule for when a thing leaves the roadmap

docs/ was ten files where a plan, a description, a guide and a bug report all
sat next to each other. It is now architecture/ (what SchOS is), plan/ (what it
will be), guides/ (how to work on it) and history/ (why it is like this), with
an index that states the one rule holding it together: when something is
finished it moves from plan/ to architecture/ and is rewritten as a description
of the thing rather than a record of building it.

A ticked checkbox says the work happened. It does not say what the work
*produced*, and six months later the checkbox is all that is left. The network
stack proved the point: finished, verified end to end, and for a month the only
description of it anywhere was a checkbox four levels of indentation deep.

So roadmap.md went from 534 lines to 181 -- nothing deleted, the done work
graduated. Seven subsystems that were finished and undescribed now have
descriptions: boot, kernel, syscalls, filesystem, networking, graphics, usb,
init. Every one ends with "What it does not do", which is the section that pays;
a document listing only strengths is marketing, and the reader who needs it most
is the one about to trip over a limitation nobody wrote down.

schfs.md still opened with "phases 1 through 3 1/2 are done, phase 4 is next"
long after all five had landed. It is a description now, with the phase record
and the hard-won bugs moved to history/.

Three corrections found on the way, all load-bearing:

  * projects/schcom/README.md claimed SCM_RIGHTS was done. There is no
    sendmsg/recvmsg in the kernel at all, and an entire GUI plan rested on it.
  * The root README said "No TCP/IP" months after the stack landed.
  * history/kernel.md sec.7 was marked "in progress" on a problem that process
    groups solved.

Also adds plan/1.0.md, which draws a finish line so the open list stops being
infinite, and marks schwm/ and schde/ superseded: in Wayland the compositor is
the window manager, so that split dissolves rather than being abandoned.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2

docs/history/README.md

@@ -0,0 +1,54 @@
+# History
+
+**Why SchOS is the way it is.** Bugs whose cause was nowhere near their symptom,
+and the few write-ups that have nowhere better to live.
+
+| | |
+|---|---|
+| [kernel.md](kernel.md) | The expensive ones. Boot, SMP, signals, ABI assumptions, `/proc`, input. |
+| [schfs.md](schfs.md) | How the filesystem was built, and what each phase cost. |
+| [moving-to-linux.md](moving-to-linux.md) | The Windows-to-Fedora move. |
+
+---
+
+## What belongs in here
+
+> **A bug whose cause is not visible from the code that fixed it.**
+
+That is the whole test. If reading the fix explains the problem, the fix is the
+documentation and nothing needs writing down. If the fix looks arbitrary — a
+constant moved by eight, a field reordered, a check inverted — then the
+strangeness is load-bearing and the next person to touch it deserves to know
+why before they change it back.
+
+Every entry here is a thing that looked like a different problem than it was.
+
+## What does not belong
+
+- **A changelog.** `git log` is the changelog.
+- **A bug that was found and fixed in an hour.** Cost is the filter.
+- **How something works.** That is [../architecture/](../architecture/), written
+  in the present tense for somebody who does not care what it used to be.
+- **Anything still open.** An unfinished investigation goes in
+  [../plan/](../plan/) or in the code as a comment. This directory is past tense.
+
+## How to write one
+
+**Symptom first, then diagnosis, then the fix, then the transferable part.**
+
+The transferable part is the reason the entry exists. `__thread` being wrong for
+per-CPU data is worth more than the specific null dereference it caused;
+"a layout constant that several artifacts must agree on wants a check that stops
+the build, not a comment asking people to remember" is worth more than the
+bootloader offset that taught it.
+
+**Say how it was found**, when the technique was the hard part. A hardware
+watchpoint through QEMU's gdb stub named an instruction on the first run after
+three rounds of `cprintf` had narrowed it to nothing — that is reusable, and the
+bug is not.
+
+**Do not clean up the embarrassing part.** The near-miss where a change passed
+every assertion green *without having been applied at all* is one of the most
+useful entries in this directory, and it only works because it admits that a
+`grep` returning three hits was read as confirmation without counting what they
+were.