Harness spec: one path form, the file tools' texts, the list tree, skills

filesystem.md, spec 3.0.0-draft, and the CLI made to match:

- Paths: absolute in every answer except a result's bracket (context.md),
  which keeps the call's path. glob and grep now give full paths.
- A missing file is `No such file or directory: {path}` for every tool
  that needs it, with no hint after it: in a chat a hidden file must read
  as a missing one. The CLI's "does not exist. Use write to create it." and
  "Write it first." are gone; an edit of a directory is `Is a directory`,
  glob over a file `Not a directory`.
- write/edit refusals, exactly: "{path} exists and has not been read in
  this session. Read it first." and "{path} changed since you last read
  it. Read it again before changing it." (no "on disk"), absolute path.
- A listing sorts names in code-point order; `list` with a depth is a
  tree indented two spaces a level, marks as in a single listing, cut at
  400 lines with a line saying so.
- Skills: where they are found and in what order on each side (the
  session's own place first, the person's next, what is shared last), and
  the name rule ^[a-z0-9][a-z0-9-]{0,63}$ that skill_manage checks. The
  CLI no longer makes names with _ or .; such skills still load.

README's 3.0.0 notes say so; CHANGELOG [Unreleased].

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/results.test.ts

@@ -45,7 +45,7 @@ test("an unchanged re-read is a stub; after an edit the file is read in full; a
   expect(r[0]).toMatch(/^\[#0001 a\.txt lines 1-3 of 3 sha ([0-9a-f]{8})\]\n1: one\n2: two\n3: three$/)
   const sha = /sha ([0-9a-f]{8})/.exec(r[0]!)![1]
   expect(r[1]).toBe(`[#0002 a.txt lines 2-2 of 3 sha ${sha}] Unchanged since #0001, which already shows lines 1-3.`)
-  expect(r[2]).toBe("[#0003]\na.txt")
+  expect(r[2]).toBe(`[#0003]\n${join(dir, "a.txt")}`)
   expect(r[3]).toBe("[#0004] Same result as #0003.")
   expect(r[4]).toMatch(/^\[#0005 a\.txt sha [0-9a-f]{8}\]\n@@ -1,3 \+1,3 @@\n one\n-two\n\+2\n three$/)
   expect(r[5]).toMatch(/^\[#0006 a\.txt lines 1-3 of 3 sha [0-9a-f]{8}\]\n1: one\n2: 2\n3: three$/)