zarvis: codex-style minimal tool surface (shell + edit_file + write_stdin)

[edwin-zvs]

What

Replaces zarvis's granular filesystem tools with a codex-style minimal coding
surface — three tools — keeping all agentd-control, subagent, and browser tools.

• Before (fs/shell coding tools): shell, read_file, write_file, edit_file, list_dir, find_files
• After: shell, edit_file, write_stdin

Why

Benchmark analysis (DeepSWE, gpt-5.5, same Codex-OAuth backend, only the harness
differs) showed zarvis issuing ~1.2× codex's tool calls but ~1.9× the model
round-trips. A big driver is the tool surface: codex exposes essentially a
shell (exec_command) + a multi-hunk patch editor (apply_patch), so the same
work maps to fewer, denser calls. zarvis's granular read/edit/list tools fan out
into many small serial calls — on one task, 62 single-hunk edits + 38 re-reads
of 5 files vs codex's 17 multi-hunk patches. This change aligns zarvis with
codex's surface.

Changes

• edit_file → multi-hunk + create. Pass edits: [{find, replace, path?}]
  applied in order (each find matches the file as modified by earlier hunks),
  validated up-front and applied atomically — a single failed match writes
  nothing. An empty find on a non-existent path creates the file,
  absorbing write_file. The single {path, find, replace} form still works.
• Persistent process subsystem (tools/proc.rs) + write_stdin. shell
  gains interactive: true: instead of killing a process at the timeout it keeps
  it alive and returns a session_id after a brief wait. The new write_stdin
  tool writes to that process's stdin (optional eof) and drains incremental
  output. A ProcRegistry is shared across the session's ToolCtxs; children
  are killed when the session ends (kill_on_drop).
• Reads/search/list via shell. Removed read_file, write_file,
  list_dir, find_files; the model uses cat/sed -n/rg/ls. Both system
  prompts updated to steer toward batched reads and multi-hunk edits.
• Kept: agentd-control (agentd_*), subagent (agentd_subagent_*), browser.

Notes / decisions

• find_files wasn't in the explicit remove list but is dropped here for
  true 3-tool parity (a search convenience now covered by rg/find in
  shell). Trivial to restore if you'd rather keep it.
• write_stdin uses pipes, not a PTY. Line-oriented programs and prompts
  work; full-screen / TTY-detecting programs may behave differently. PTY
  allocation is a possible follow-up.
• Atomicity is guaranteed at the match-validation stage (no partial application
  on a bad find); cross-file write failures are I/O-only and reported.

Tests

144 pass (8 new): proc sessions (echo / exit / unknown id), multi-hunk
apply-in-order, atomic-on-failure, empty-find create, single edit, and an
interactive shell + write_stdin round-trip. Updated the auto-approve test
(write_file → edit_file) and the skills prose test.

Relevant binary: agentd-adapter-zarvis — this PR only touches
crates/adapter-zarvis; agent / agentd / agentd-mcp build unchanged.

🤖 Generated with Claude Code