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# Generated-buffer immutability
**PROPOSED — needs explicit user approval before implementation. DO NOT
implement, DO NOT merge.**
**Revision 1 — scouted against canonical `githubsucks/main` @ `ad41cf1`,
2026-07-28. Every claim below about pmacs was executed, not read.** The
reproductions in §0 are transcripts of throwaway probes run in this
worktree at `ad41cf1` and deleted before the commit; the counts in §1
are whole greps with the arithmetic shown, never `| head`.
This closes the class-wide half of the invariant `Buffer::set_generated_contents`
opened in terminal copy mode (#178) and that `docs/agent-handoff.md` §4 and
`COHERENCE.md` §14 both record as unfinished: **four writer mechanisms across
five buffer families still pair an erroring intercept with `bypass_intercept`
writes over a writable rope, and every one of them is emptied by undo.**
Two things the arc turns out NOT to be, both discovered by measurement:
- It is **not** "compile is the urgent one". `compile.lua` and the
`*search-results*` panel rebind all seven undo chords to a no-op
(`compile.lua:219`, `builtin/commands/default.lua:855`), so reaching
them needs `M-x`. **`dired.lua` and `listview.lua` rebind nothing**, so
a bare `C-/` empties them. The cheap half is also the exposed half.
- It is **not** a Lua-only change. Two of the four mechanisms write
incrementally and cannot use the shipped primitive at all, and a
buffer the shipped primitive has locked **refuses `bypass_intercept`
writes** (§2.4, measured) — so partial adoption is impossible and a
new Rust primitive is required.
---
## 0. The bug, reproduced
`Buffer::undo` (`src/buffer.rs:1301`) gates on `ensure_writable()`
(`src/buffer.rs:568`) and nothing else. `ensure_writable` reads the Rust
`read_only` field; it never consults the intercept chain. The
`pmacs.buffer.add_intercept(buf, function() error(name .. " is read-only") end)`
idiom therefore protects the *edit* path and leaves the *history* path
wide open, while the owner's own `bypass_intercept` paint lands on the
undo stack for undo to pop.
The user-reachable chain, verified end to end:
`M-x buffer.undo` → `cmd { name = "buffer.undo" }`
(`builtin/commands/default.lua:179`) → `ed.undo()` → `EditorCore::undo`
(`src/editor_core.rs:2575`) → `Buffer::undo` → `ensure_writable`. The
chords `C-/ C-_ C-4 C-x u` are bound globally
(`builtin/keymaps/default.lua:126-136`) and the menu carries it too
(`builtin/menus/default.lua:141`). **No buffer-local rebinding removes
the command**, which is what `compile.lua`'s own comment already admits
("command/menu undo stays dispatchable", `compile.lua:236`).
### 0.1 Measured transcripts
Every line below is probe output from `ad41cf1`.
**listview panel, plain `C-/` through `dispatch_key`** — no rebinding
exists, so this is the whole distance from a keystroke to an empty panel:
```
listview BEFORE = "H\nrow-one\nrow-two"
listview after C-/ = ""
```
**listview panel, ordinary edit** — the intercept works, which is exactly
why the idiom reads as safe:
```
listview ORDINARY EDIT = false | intercept rejected the edit:
builtin/runtime/listview.lua:102: *probe-panel* is read-only
```
**dired listing, one `buffer.undo`:**
```
dired BEFORE = "/tmp/.tmpEJlp9i:\n -rw-r--r-- 1 2026-07-28 17:42 alpha.txt\n -rw-r--r-- 1 2026-07-28 17:42 beta.txt"
dired AFTER 1 = ""
```
**`*shell-command*`, `M-x buffer.undo` through the real minibuffer** (`M-x`,
typed `buffer.undo`, RET):
```
shell BEFORE = "$ printf ...\nDirectory: ...\n\none\ntwo\n\n[shell exited with code 0]\n"
shell after M-x buffer.undo
= "$ printf ...\nDirectory: ...\n\none\ntwo\n\n[output desynced by external edit]\n"
```
**Read that one carefully — it is the single most important measurement in
this document.** The Q#CM2 revision guard *noticed* and appended its
desync marker. It did **not** prevent anything: the run's exit status is
gone for good, and the buffer is still non-empty. Any acceptance
criterion phrased as "the buffer is not empty" **passes with the bug
live**. See §5, Stage 2 criterion 1.
Driven programmatically to the end, the same buffer empties completely:
```
shell AFTER 1 undo = "... one\ntwo\n" (exit marker gone)
shell AFTER 13 undos = ""
```
**`*search-results*`:**
```
search BEFORE = "Searching for: fn main\n\n"
search AFTER = ""
```
### 0.2 The fix already in the tree, and what it proves
`terminal.lua` is the adopter and the precedent. `render_snapshot`
(`terminal.lua:320-337`) calls `pmacs.buffer.set_generated_contents`, and
the comment at `:322-336` documents this exact defect in these exact
terms. `claim_snapshot` (`:339-396`) keeps the erroring intercept **and**
`set_round_trip_input`, and `:351-366` states the layering that this
framing must preserve at every adopter:
> rope-level read-only protects the daemon copy, round-trip input
> protects the replica copy — and neither substitutes for the other.
A locked buffer measured at `ad41cf1`:
```
bypass write after lock = false | buffer `*probe*` (id BufferId(4)) is read-only
M-x buffer.undo after lock leaves = "header\n"
```
---
## 1. The census, with its arithmetic
### 1.1 `bypass_intercept` — 21 grep hits, 16 write sites
`grep -rn bypass_intercept builtin` returns **21** lines. Five of them
are prose in comments, not calls:
| file:line | what it is |
|---|---|
| `compile.lua:265` | comment above `ensure_slot`'s intercept |
| `terminal.lua:304` | comment in `unique_snapshot_name` |
| `terminal.lua:324` | comment in `render_snapshot` (the round-2 note) |
| `dired.lua:478` | comment above `claim_handle` |
| `listview.lua:9` | module header |
21 − 5 = **16 actual write call sites**, and the per-file arithmetic is
9 + 4 + 1 + 2 + 0 = 16:
| file | writes | lines |
|---|---|---|
| `compile.lua` | 9 | 319, 443, 454, 465, 506, 512, 642, 794, 798 |
| `builtin/commands/default.lua` | 4 | 827, 849, 1005, 1007 |
| `dired.lua` | 1 | 371 |
| `listview.lua` | 2 | 60, 61 |
| `terminal.lua` | **0** | — (it adopted the primitive) |
**Two corrections to the counts this lane was briefed with.** `compile.lua`
has **9** write sites, not 10 — the tenth hit is the comment at `:265`.
`terminal.lua`'s two hits are **both comments**; it performs no
`bypass_intercept` write at all, which is the correct state for an
adopter and is worth stating because the raw grep count reads as though
it still does.
### 1.2 `add_intercept` — 17 Lua sites, 6 production
`grep -rn --include='*.lua' add_intercept . --exclude-dir=target`
returns **17** lines: **6** in `builtin/`, **11** under `tests/fixtures/`.
One of the eleven (`tests/fixtures/pmacs-mcp-prompts/init.lua:84`) is a
doc comment, so the fixture *call* count is 10; 6 + 10 = 16 calls across
17 lines. The six production sites:
| site | buffer(s) | shape |
|---|---|---|
| `terminal.lua:367` | terminal copy snapshot | blanket read-only — **adopted** |
| `dired.lua:509` | every dired buffer | blanket read-only |
| `listview.lua:101` | every listview panel | blanket read-only |
| `compile.lua:266` | `*compilation*`, `*shell-command*` | blanket read-only |
| `builtin/commands/default.lua:869` | `*search-results*` | blanket read-only |
| `builtin/packages/repl/init.lua:187` | REPL buffers | **filtering** — §2.5 |
### 1.3 `set_read_only` — zero Lua callers, and no Lua binding
`grep -rn set_read_only builtin tests` returns 5 hits, **all Rust test
code** (`tests/folding_acceptance.rs:587`,
`tests/vterm_stage1_acceptance.rs:139,175`,
`tests/terminal_copy_mode_acceptance.rs:582,584`). The stronger fact:
the Lua binding table registers `"add_intercept"` and no
`"set_read_only"` / `"is_read_only"` at all
(`src/lua_bindings/mod.rs:3409` is the only match in the neighbourhood).
Lua *cannot* set `read_only` today. That matters for Q#GB7.
### 1.4 The classification, by writer mechanism
**Class A — erroring intercept + `bypass_intercept` writes over a
writable rope. This is the bug.**
1. **`terminal.lua`** — copy-mode snapshot. **ADOPTED** (`:336`). Fixed.
2. **`dired.lua`** — every dired buffer. One write, in `paint`
(`:369-372`): `handle.buf:replace(0, handle.buf:len(), text, {bypass_intercept=true})`.
A whole-buffer replace already. **Convertible with the shipped
primitive.**
3. **`listview.lua`** — `*references*`, `*outline*`, `*lsp-help*` (the
three production `listview.open` callers, all in `lsp.lua`:2056, 2102,
2513). One writer, `render` (`:50-62`): delete-all then insert-all,
which is a whole-buffer replace spelled in two ops.
**Convertible.**
4. **`compile.lua`** — `*compilation*` and `*shell-command*`, both via
`ensure_slot` (`:258`). Nine writes across five enclosing functions,
and they are genuinely incremental:
| enclosing function | line | shape |
|---|---|---|
| `resync` (`:309`) | 319 | append desync marker at end |
| `emit_text` (`:432`) | 443 | append remainder at end |
| `emit_text` | 454 | append `"\n"` at end |
| `emit_text` | 465 | **positional `replace`** (CR overwrite) |
| `apply_events` (`:480`) | 506 | **targeted delete** (erase-to-eol) |
| `apply_events` | 512 | **targeted delete** (erase-line) |
| `emit_text_raw` (`:639`) | 642 | append marker at end |
| `start_run` (`:746`) | 794 | delete-all (run reset) |
| `start_run` | 798 | insert header (run reset) |
**NOT convertible.** `emit_text` is a terminal emulator: it tracks
`slot.out_pos` / `slot.line_start` / `slot.parse_line_start` as byte
anchors, reads `buf:slice(pos, len)` between writes, and settles
`slot.expected_rev = buf:revision()` afterwards. A whole-buffer
replace destroys every one of those anchors.
5. **`builtin/commands/default.lua`** — the independent `*search-results*`
panel (`ensure_search_panel`, `:857`). Four writes across three
enclosing functions:
| enclosing function | line | shape |
|---|---|---|
| `search_panel_resync` (`:821`) | 827 | append desync marker |
| `search_panel_append` (`:844`) | 849 | append match batch |
| `pmacs.project.search` (`:982`) | 1005 | delete-all (query reset) |
| `pmacs.project.search` | 1007 | insert header (query reset) |
**NOT convertible**, for the same reason at smaller scale: the append
path carries `p.next_row` / `p.expected_rev` bookkeeping.
**Do not read `ensure_slot` as covering this panel.** It serves
`*compilation*` and `*shell-command*` only; `*search-results*` has its
own intercept, its own round-trip mark, its own resync and its own
writes, and `compile.lua` names it only inside the
`is_generated_buffer` predicate (`:216`).
**Class B — filtering intercept, deliberately partly editable.**
6. **`builtin/packages/repl/init.lua:187`** — see §2.5. Shares the root
cause, does not share the remedy. **Out of this arc.**
**Class C — generated, but nothing ever claimed they were protected.**
Keying the inventory on `bypass_intercept` misses these entirely,
because an unprotected buffer needs no bypass:
7. **`*buffer-list*`** — `render_list` (`default.lua:387`) writes with
plain `buf:delete(0, len)` / `buf:insert(0, body)` (`:403-404`). No
intercept, no round-trip mark. Whole-replace shape.
8. **`*help*`** — `show_help_text` (`default.lua:1239`), same plain
delete-all + insert-all (`:1245-1246`). No intercept.
9. **`*workers*`** — a **Rust** writer, `workers_buffer::render`
(`src/workers_buffer.rs:65`), using `Buffer::apply_edit` (not the
skip-intercepts path), delete-all + insert-all, then
`Buffer::mark_clean()` (`:95`). Its fan-out is a fourth mechanism:
`queue_generated_buffer_edits` + `rebuild_generated_buffer_views`
(`src/lua_bindings/mod.rs:7142-7145`).
Class C is a **different defect** — nothing is defeated, because nothing
was claimed. It is named here so the inventory is complete and so a
future reviewer does not re-derive it; §4 keeps it out of this arc.
### 1.5 A correction to `COHERENCE.md` §14 (not edited here)
§14 states that "references, outline, buffer-list, and project-search all
use" listview. Measured: `pmacs.listview.open` has **three** production
callers, all in `lsp.lua` — `*references*` (`:2056`), `*outline*`
(`:2102`), `*lsp-help*` (`:2513`). `*buffer-list*` is hand-rolled in
`default.lua` (`render_list`, `:387`) and `*search-results*` is the
independent grep panel. Two of §14's four examples are wrong, and
`*lsp-help*` is missing. `COHERENCE.md` is not this lane's file to edit;
recorded here and in the PR body.
---
## 2. Ground truth (measured, not recalled)
### 2.1 What the shipped primitive is
`Buffer::set_generated_contents` (`src/buffer.rs:545`, doc comment
`:507-544`): lift `read_only`, `apply_edit_skip_intercepts` a **single
whole-buffer** `EditOp::Replace`, `clear_history()` (`:559`), re-assert
`read_only`, **return the `Edit`**. The Lua binding
(`src/lua_bindings/mod.rs:3079-3095`) fans that `Edit` out via
`notify_buffer_edit_to_windows` (`:1573`) *after* dropping the registry
borrow, because the fan-out re-enters the core.
`clear_history` clears whichever history the buffer has: the v0.1
`undo`/`redo` stacks, and in CRDT mode `CrdtState::clear_undo_history`
(`src/crdt.rs:507`), which rebinds a fresh `UndoManager` to the same doc
because loro exposes no `clear`.
### 2.2 Why history clearing is load-bearing
The doc comment's reason is retention, not tidiness: `read_only`
guarantees the pushed entries can never be popped, so a periodically
refreshed panel accumulates full rope clones nothing will ever release.
CRDT mode has the identical retention inside loro's `UndoManager`.
### 2.3 Why a bare lock is not the answer
`ensure_writable` guards the bypass path too
(`apply_edit_skip_intercepts`, `src/buffer.rs:1055-1056`). Locking a
generated buffer without giving its owner a door refuses the refresh the
buffer exists for. That is why the *pairing* is the primitive and why
there is deliberately no Lua `set_read_only` today.
### 2.4 Partial adoption is impossible — measured
This is the fact that decides the design. Once `set_generated_contents`
has locked a buffer, a subsequent owner write through `bypass_intercept`
is refused:
```
bypass write after lock = false | buffer `*probe*` (id BufferId(4)) is read-only
```
So compile **cannot** convert its run reset (`start_run:794,798`) to the
shipped primitive and keep `bypass_intercept` for streaming: the first
append after the reset raises. The streaming owner needs a write path
that *itself* carries authority. Reads are unaffected — `buf:slice`,
`buf:len` and `buf:revision` all work on a locked buffer, which is what
makes an op-level solution viable at all.
### 2.5 The REPL: same root cause, different remedy — measured
`builtin/packages/repl/init.lua:187` installs
`function(op) return repl._intercept(h, op) end` — a **filtering** policy
(`repl._intercept`, `:686-726`): reject edits wholly inside the
history/prompt region, **truncate** edits that straddle the boundary,
pass edits in the input region. Its own writes use a `_self_write` flag
(`with_self_write`, `:111-116`) rather than `bypass_intercept`, and it
has real teardown (`remove_intercept`, `:325-327`).
Does it share the bug? **Yes — measured — and I am not asserting the
comfortable answer:**
```
repl BEFORE = "line one\nline two\n> "
repl ordinary edit at pos 0 = false | REPL: history/prompt region is read-only
(insert at 0; input region begins at 20)
repl AFTER 1 buffer.undo = "line one\nline two\n"
repl bookkeeping after undo = _history_end=18 / _prompt_end=20 (rope is 18 bytes)
```
Undo deleted the prompt the intercept had just refused to let anyone
touch, and left `_prompt_end` pointing two bytes past the end of the
rope. The marks (`_history_end_mark`, `_prompt_end_mark`) adjust with the
rope, but `_blocks[i].start_byte` are plain integers maintained by hand
in `drop_oldest_block` (`:643-656`) and do not.
**But the remedy cannot be rope-level `read_only`**: the input region
must accept ordinary user edits, which is the whole point of a REPL. The
REPL needs either an undo that consults the intercept chain, or
mark-anchored blocks. Both are different work. **Q#GB8: out of this arc,
named deferral, with its measurement recorded above so the next lane does
not have to rediscover it.**
### 2.6 A pre-existing defect in the shipped primitive — measured
`notify_buffer_edit` (`src/editor_core.rs:1814`) updates each window's
`TextView` and overlays. It does **not** clamp `win.cursor` or
`win.view_top`. Only `rebuild_views_for` (`:1843`) does, and its doc
comment says so explicitly (`:1841-1842`). `set_generated_contents`'s
binding calls the former.
```
cursor before = 29, len = 30
cursor after set_generated_contents(G, 'x\n') = 29, len = 2
row0 after shrink = "x" (paint did not crash)
cursor after C-p = 29 (motion did not recover it)
```
A shrinking generated write leaves the window cursor 27 bytes past the
end of the buffer, indefinitely. **This ships today in terminal copy
mode** — refresh a snapshot to a shorter one with the point low in the
buffer and this is the state — and every adopter inherits it. Q#GB6.
### 2.7 What `buffer.after-edit` does and does not do
`buf:insert` / `buf:delete` / `buf:replace` do **not** fire
`buffer.after-edit`; the dispatcher and daemon do
(`src/editor.rs:1436,1984,2128,2163`, `src/daemon.rs:2976`).
`compile.lua:714` already relies on this ("hook edits don't re-fire the
hook"). Consequence for §3: a generated write does not run arbitrary Lua,
so the *fan-out* is not a re-entrancy hazard — but a scoped primitive's
**callback body** still is, because it is arbitrary owner Lua.
---
## 3. The primitive decision (Q#GB1)
**The question this arc exists to answer: what write primitive do
`compile.lua` and the search panel need?**
### 3.1 Recommendation
**`Buffer::apply_generated_edit(op: EditOp) -> Result<Edit, BufferError>`
— one authorized op at a time — exposed to Lua as a new option key on
the mutators that already exist:**
```lua
buf:insert(pos, text, { generated = true })
buf:delete(start, end_, { generated = true })
buf:replace(s, e, text, { generated = true })
```
Semantics, per call, entirely inside one `with_registry_mut`: lift
`read_only` → `apply_edit_skip_intercepts(op)` → `clear_history()` →
re-assert `read_only` → return the `Edit`. The binding then fans it out
through the `notify_buffer_edit_to_windows` call it **already makes**
(`src/lua_bindings/mod.rs:1291`, `:1302`, `:1322`), after the borrow has
dropped.
`Buffer::set_generated_contents(bytes)` is reimplemented as
`apply_generated_edit(Replace { range: 0..len, bytes })`. **It keeps its
name, its signature, its doc comment and its tests** — it becomes the
whole-buffer spelling of one primitive rather than a second primitive.
**One sentence for why it wins: it is the only candidate in which the
buffer is never observably unlocked, because the lift and the re-assert
happen inside a single registry borrow with no Lua in between — so there
is no flag to clear on an error path, no yield to defend against, and
nothing for a reviewer to audit site by site.**
### 3.2 Why the alternatives lose
**A. `append_generated_contents` — provably insufficient.** `compile.lua`
does a positional `replace` at `emit_text:465` (the CR overwrite that
makes progress bars work) and two targeted `delete`s at
`apply_events:506,512` (erase-to-eol, erase-line). Append cannot express
any of the three. Dead on the census.
**B. Scoped `with_generated_writes(buf, fn)` — the pattern this project
has already been burned by.** It is the cheapest on history (one
`clear_history` per scope instead of one per op) and that is its only
real advantage. Against it:
- **The unlocked interval is the callback's whole duration, and the
callback is arbitrary owner Lua.** Drawn loosely around `start_run`
(`compile.lua:746`), the scope spans `pmacs.window.switch_buffer(buf)`
and `pcall(pmacs.process.spawn, spec)` — the buffer would be writable
across a process spawn. Drawn tightly, compile needs four separate
scopes (`start_run`'s reset, `resync`, `feed_bytes`, `finish_run`), each
needing its own audit for what the body reaches.
- **Correctness reduces to "a flag cleared on every exit."** That is the
exact shape `docs/agent-handoff.md` §5 and #155 record as a repeat
offender, and the REPL already had to defend its own version of it:
`with_self_write` (`repl/init.lua:111-116`) wraps in `pcall`
specifically because "a single failed write would leave the bypass on
for every subsequent user edit". Adding a second instance of a pattern
the tree already documents as fragile is a poor trade for one saved
`clear_history` per batch.
- **Yield is an error here, which helps but does not rescue it.** A Lua
callback that yields across the Rust boundary raises
`attempt to yield across C-call boundary` (observed in this worktree
while probing `pmacs.dired.open`), so a yielding body surfaces as
`Err` — but the relock must still run on that path, which is the same
obligation.
- It is strictly harder to review: a per-site scope audit versus a
mechanical option-key change at 16 call sites.
**C. Standalone `generated_edit(buf, op)`.** Identical semantics to the
recommendation, worse ergonomics: it re-implements the three-op argument
parsing that `buf:insert/delete/replace` already own, and turns adoption
from an option-key change into a rewrite of 16 call sites. Recommended
only if the user objects to `{ generated = true }` sitting beside
`{ bypass_intercept = true }` in the same options table.
**D. Make `Buffer::undo`/`redo` consult the intercept chain.** This would
fix all six families at once, including the REPL, and it deserves an
explicit rejection rather than silence. Against it: (i) there is no
`EditOp` to hand the chain — v0.1 undo is a whole-rope swap
(`src/buffer.rs:1327-1328`) and CRDT undo is materialize-and-replace
(`undo_crdt_mode`, `:1365`), so the chain would have to be given a
synthetic op it was never designed to see; (ii) it changes behaviour for
every intercept in the tree, including the *transforming* ones
(auto-pair, lean-input, the REPL's truncation) which have no business
rewriting an undo; (iii) an erroring intercept becomes a new Lua-raise
failure path out of `EditorCore::undo`, which today cannot fail that way.
It may still be the right answer **for the REPL specifically** — recorded
in Q#GB8's deferral, not adopted here.
### 3.3 The four questions the recommendation must answer
**How many `Edit`s are fanned out, and when?** One per generated op,
immediately, by the binding that already does it. `compile.lua`'s
`emit_text` fast path emits one insert for a whole output batch, so a
typical `feed_bytes` produces one to three ops; a CR-heavy progress bar
produces more. This is exactly today's fan-out count — the conversion
changes authority, not cardinality.
**Per-op or per-scope history clearing?** Per op, and it is cheap by
construction: because `read_only` is re-asserted immediately, **at most
one** v0.1 undo entry can exist when the clear runs and the redo stack is
always empty, so the v0.1 clear is O(1). In CRDT mode the clear rebinds
a fresh `UndoManager` (`CrdtState::clear_undo_history`), and
`create_undo_manager` (`src/crdt.rs:154`) is `UndoManager::new(doc)` plus
`set_max_undo_steps` — a subscription registration, not a document copy,
so it is O(1) in document size too. **Measurement obligation, not a
claim:** Stage 2 must show a streaming compile run does not regress
against the existing compile-mode timings in both configurations. If it
does, the escape hatch is to suppress recording rather than clear it —
recorded as a named deferral rather than designed speculatively.
**CRDT-mode behaviour?** Identical to `set_generated_contents` today. The
`Edit` carries `crdt_op` when the buffer is CRDT-backed, and
`notify_buffer_edit_to_windows` queues it via
`queue_daemon_origin_crdt_op` (`src/lua_bindings/mod.rs:1582`) so replica
mirrors import the owner's write. History clearing goes to loro's
`UndoManager`. Nothing new.
**How do the returned edits reach the fan-out without a live registry
borrow?** By construction, unchanged since #178: `run_bypass_edit`
(`src/lua_bindings/mod.rs:1445`) closes its `with_registry_mut` before
returning, and the mutator bindings call
`notify_buffer_edit_to_windows` afterwards. `apply_generated_edit` slots
into the same place `apply_edit_skip_intercepts` occupies now.
---
## 4. Decisions
**Q#GB1 — The streaming primitive.** `Buffer::apply_generated_edit(op)`,
exposed as `{ generated = true }` on the three Lua mutators.
`set_generated_contents` becomes its whole-buffer wrapper, keeping name,
signature and tests. Rationale and rejected alternatives: §3.
**Q#GB2 — `generated` is additive; `bypass_intercept` stays.** Seven
call sites outside `builtin/` depend on `bypass_intercept`, including
`tests/folding_stage2_acceptance.rs:1296-1315`, which pins that a bypass
edit still triggers the Q#FD19 interactive unfold. Redefining the
existing key would silently change that pinned seam. `generated = true`
implies bypass; passing both is legal and `generated` wins (it is
strictly stronger); passing `generated` on a buffer with no intercept is
legal (Class C would use it if it ever adopts).
**Q#GB3 — Routing is otherwise identical to bypass.** A generated write
goes through `run_buffer_edit`'s bypass arm (`src/lua_bindings/mod.rs:1368`),
including `unfold_before_interactive_lua_edit`. The unfold guard already
requires `InteractiveCommandOrigin::current()` to be `Some`, which is
false for the `process.after-tick` pump and true for `M-x compile`;
folding a `*compilation*` buffer is possible, so changing this would be a
silent behaviour change to a pinned seam for no reason this lane owns.
**Q#GB4 — History cleared per op, with a measurement obligation.** §3.3.
Deferred optimization: suppress recording instead of clearing.
**Q#GB5 — The lock-at-creation gap, and who closes it.** A
`{ generated = true }` write locks the buffer *after* its first call, so
between `pmacs.buffer.create(name)` and the owner's first generated write
the rope is writable. `dired.lua` (`claim_handle` → `paint`),
`listview.lua` (`ensure_panel` → `render`) and the search panel
(`ensure_search_panel` → the header write in `pmacs.project.search`) all
write synchronously in the same call, so the window is not observable.
**`compile.lua`'s `ensure_slot` (`:258-282`) does not** — it creates
`*compilation*` and returns, leaving it empty and writable until
`start_run`. Recommendation: `ensure_slot` ends with
`pmacs.buffer.set_generated_contents(slot.buf, "")`, using the shipped
primitive; no third surface is needed. Note the pre-existing hazard this
inherits and does not create: `ensure_slot` is
`buffer_named(name) or create`, so it can adopt a foreign buffer, which
`start_run:794`'s delete-all already clobbers today.
**Q#GB6 — Clamp the window cursor on a generated write.** §2.6 measures a
shipped defect: a shrinking generated write leaves `win.cursor` past the
end of the rope, and neither paint nor `C-p` recovers it. Recommendation:
clamp `win.cursor` and `win.view_top` in `EditorCore::notify_buffer_edit`
when the buffer shrank — a **clamp**, not a call to `rebuild_views_for`,
because a rebuild is O(buffer length) and would run per streaming op.
Recommended for **Stage 1**, because Stage 1's adopters refresh shrinking
panels constantly and because it fixes terminal copy mode retroactively.
Alternative if the user prefers a narrower Stage 1: its own lane, in
which case Stage 1 must say so out loud rather than inherit it silently.
**Q#GB7 — wdired needs an unlock, and Lua cannot express one.** Dired
Stage 3 (`docs/dired-framing.md` §5) makes a dired buffer editable by
removing the read-only intercept and swapping the major mode. Once
dired's rope is `read_only`, removing the intercept is no longer
sufficient — and §1.3 measured that **no Lua binding can clear
`read_only`**. Recommendation: **name it, do not build it.** A binding
whose only consumer does not exist yet cannot be pinned against a real
caller, and "asserting that a value was stored is not asserting that
anything reads it" is a lesson this repo has already paid for. Stage 1
records it as a hard prerequisite on dired Stage 3's framing.
If the user rules the other way, the two shapes are: expose
`pmacs.buffer.set_read_only(buf, on)` — which **contradicts
`docs/agent-handoff.md` §4's "there is deliberately no Lua
`set_read_only`"**, and needs an explicit ruling rather than a quiet
addition, though the objection behind that invariant ("it also refuses
the owner's refresh") is answered once `{ generated = true }` ships — or
a one-way `pmacs.buffer.unlock_generated(buf)`, strictly weaker because
it can never lock anything.
**Q#GB8 — The REPL is out of this arc.** §2.5. Same root cause, different
remedy, its own lane. Its measured exposure is recorded above so the next
scout starts from evidence.
**Q#GB9 — Class C is out of this arc.** `*buffer-list*`, `*help*` and
`*workers*` are generated but were never claimed to be protected, so
nothing about them is *defeated*. Making them immutable is a product
decision about `COHERENCE.md` §14's list and output-channel primitives,
not a bug fix, and it should not ride a bug-fix arc. `*workers*`
additionally writes from Rust with its own fan-out pair and already
`mark_clean`s, so it is not a like-for-like conversion.
**Q#GB10 — Mark generated buffers clean.** `set_generated_contents`
leaves `is_modified = true` (measured: `modified=true` after one write),
so every adopter shows `*` in the mode line
(`src/editor.rs:3704`) and in `*buffer-list*` (`default.lua:395`).
`workers_buffer::render` calls `Buffer::mark_clean()` (`:95`) for exactly
this reason. Recommendation: `apply_generated_edit` marks clean.
**This changes shipped `set_generated_contents` behaviour** and therefore
the terminal snapshot, so it belongs in Stage 2 alongside the
reimplementation, not smuggled into Stage 1. Verified non-blocking: the
flag drives only the mode-line indicator and the buffer-list column —
`grep` finds no quit-time or kill-time prompt reading it.
**Q#GB11 — Staging.** §5.
**Q#GB12 — The revision guard becomes near-dead, and three tests break.**
After Stage 2, an external edit to `*compilation*` or `*search-results*`
is refused at the rope, so the Q#CM2 desync machinery (`check_rev`
`compile.lua:332`, `resync` `:309`, `search_panel_check_rev`
`default.lua:832`) can essentially no longer fire. Recommendation: **keep
it** — it is cheap, and a future Rust-side writer could still mutate the
buffer — but say so, and do not delete its tests. Three compile
acceptance tests inject intruder edits through `bypass_intercept`
(`tests/compile_mode_acceptance.rs:1040`, `:1106`, `:1305`) and **will be
refused** after conversion; they must lift `read_only` Rust-side first,
exactly as `tests/terminal_copy_mode_acceptance.rs:582-584` already does.
That is a concrete, verified integration cost of Stage 2, not a surprise
to discover during implementation.
---
## 5. Staging
**The proposed cut is endorsed, with two amendments.** The argument for
it is not the obvious one.
### Stage 1 — `generated-buffer-immutability-stage1`
`dired.lua` and `listview.lua` adopt `pmacs.buffer.set_generated_contents`.
No new primitive.
- `listview.lua:50-62` — `render`'s delete-all + insert-all becomes one
`set_generated_contents(buf, body)`.
- `dired.lua:369-372` — `paint`'s whole-buffer replace becomes one
`set_generated_contents(handle.buf, text)`.
- Both keep their erroring intercept (named error, per the layering at
`terminal.lua:351-366`) and both keep `set_round_trip_input`.
- Plus Q#GB6's cursor clamp, if approved.
**Why this cut, and why Stage 1 is not merely "the cheap half":** it is
the *worse-exposure* half. `compile.lua:219` and
`builtin/commands/default.lua:855` rebind all seven undo chords to
`compile.undo-noop`; `dired.lua` and `listview.lua` rebind **nothing** —
`grep -n 'C-/\|C-_\|C-x u\|undo' builtin/runtime/dired.lua builtin/runtime/listview.lua`
returns zero binding lines. Measured, a bare `C-/` empties a listview
panel and a dired listing. Stage 1 closes the only two families
reachable without `M-x`.
**Why the cut is safe under every candidate primitive:** a whole-buffer
replace is expressible in all of A–C, and under the recommendation
`set_generated_contents` keeps its name and signature as
`apply_generated_edit`'s wrapper. Stage 1 is therefore not rework under
any Q#GB1 outcome — which is the decisive argument for cutting here
rather than shipping one large PR.
**The honest objection, and the answer.** A reviewer could call Stage 1
churn: two call sites converted to a primitive Stage 2 then rewrites.
Stage 2 rewrites the primitive's *implementation*, not its callers; the
diff at `dired.lua:371` and `listview.lua:60-61` is written once.
### Stage 2 — `generated-buffer-immutability-stage2`
`Buffer::apply_generated_edit` + the `{ generated = true }` option +
`set_generated_contents` reimplemented over it + Q#GB10's `mark_clean` +
conversion of all 13 remaining write sites (`compile.lua` 9,
`builtin/commands/default.lua` 4) + Q#GB5's `ensure_slot` lock + the
three `compile_mode_acceptance` intruder tests updated per Q#GB12.
All the new Rust and all the review risk in one PR, which is the point of
the cut.
**Amendments to the briefed cut:**
1. **Q#GB7 (wdired) is recorded in Stage 1, not built in it.** Stage 1
makes dired's rope read-only, which creates an obligation for dired
Stage 3 that does not exist today. Recording it is the deliverable;
building an unlock binding with no caller is not.
2. **Q#GB10 (`mark_clean`) lands in Stage 2, not Stage 1**, because it
edits `set_generated_contents` itself and therefore changes the
already-shipped terminal snapshot. Stage 1 stays a pure-Lua change
(plus Q#GB6, if approved).
**Where the REPL lands: neither stage.** Q#GB8.
---
## 6. Acceptance, with the pre-image each criterion must fail against
`M-x buffer.undo` is the user-reachable trigger and **needs no keymap**.
A criterion that only exercises the intercept, or only the chords, proves
nothing — that is precisely what `compile.lua`'s idiom already achieves
and what this bug already defeats.
### Stage 1
1. **`C-/` cannot empty a listview panel.** Driven by `dispatch_key`,
not by a Lua call. *Bite:* on `ad41cf1` this measured
`"H\nrow-one\nrow-two"` → `""`.
2. **`M-x buffer.undo` cannot empty a listview panel**, driven through
the real minibuffer (`M-x`, type `buffer.undo`, RET) — not
`pmacs.command.invoke`, which is the programmatic path. *Bite:* same
empty result on the pre-image; and a chord-only fix passes 1 and
fails this.
3. **`C-/` and `M-x buffer.undo` cannot empty a dired listing.** *Bite:*
measured — one undo takes the listing to `""`.
4. **The owner's own refresh still works after the lock** — `g` on a
listview panel and on a dired buffer re-renders new content. *Bite:*
this is the criterion that falsifies the **obvious wrong fix**, not
the pre-image: a naive `set_read_only(true)` at creation passes 1–3
and fails here, which is the failure mode `src/buffer.rs:521-524`
exists to prevent. Assert the *new* content appears, not that the
call did not raise.
5. **An ordinary edit is still refused with the intercept's named
message.** *Bite:* deleting the intercept while keeping the rope lock
passes 1–4 and fails this; the layering at `terminal.lua:351-366`
requires the named error to survive.
6. **`set_round_trip_input` is still set on both.** Pinned ungated, via
`dispatch_idle_for` reporting **false** while the panel is focused —
the shape `tests/terminal_copy_mode_acceptance.rs` criterion 16 uses,
which needs no CRDT. *Bite:* delete the `set_round_trip_input` call
and 1–5 all still pass; only this fails. A daemon-side refusal does
nothing for a replica's own mirror.
7. **A refresh reaches the window, not just the rope** — pinned by
**painting** a shrinking render (many rows → one) and asserting row 1
is empty, for each adopter. *Bite:* not redundant with #178's
criterion 16d, because it catches a **partial** conversion — an
adopter that keeps one `bypass_intercept` write beside the primitive
— which 16d cannot see.
8. **Cursor clamp (only if Q#GB6 is approved).** After a shrinking
refresh, `pmacs.editor.cursor() <= buf:len()`, and `C-p` moves. *Bite:*
measured on `ad41cf1` — cursor 29, len 2, `C-p` leaves it at 29. This
pin **fails on `main` today**, including for terminal copy mode, which
is the evidence it is a real fix and not bookkeeping.
9. **Structural, riding alongside and never instead of 1–8:** no
`bypass_intercept` write remains in `dired.lua` or `listview.lua`.
A structural comparison of two authorities does not catch a misrouted
consumer; keep the consumer-level assertions.
### Stage 2
1. **`M-x buffer.undo` cannot destroy `*compilation*` /
`*shell-command*` / `*search-results*` content — and the criterion
must assert the *exit marker survives*, not that the buffer is
non-empty.** *Bite, and this is the whole point:* on `ad41cf1` the
measured result of `M-x buffer.undo` on `*shell-command*` is
`[shell exited with code 0]` replaced by
`[output desynced by external edit]`. The buffer is still non-empty,
so a "not empty" assertion **passes with the bug live**. The revision
guard *marks* the corruption; it does not prevent it.
2. **A streaming run's incremental writes still land**, including CR
overwrite semantics (a progress-bar fixture) and erase-to-eol. Assert
the produced content, not the absence of an error. *Bite:* the
pre-image is the tempting half-conversion — reset via
`set_generated_contents`, stream via `bypass_intercept` — which raises
`is read-only` at the first append (measured, §2.4).
3. **The buffer is locked BETWEEN batches, not only after the run.**
Attempt an ordinary edit mid-run and require the refusal. *Bite:* a
scope-shaped implementation that unlocks for a whole run passes 1 and
2 and fails this. A state predicate, not a geometric readout.
4. **History does not accumulate across a long run:** `buf:undo()`
returns false and the contents are unchanged after N batches.
5. **`ensure_slot` leaves `*compilation*` locked before any run**
(Q#GB5). *Bite:* create the slot without running anything, then
attempt an ordinary edit; without the explicit lock it lands.
6. **`mark_clean` (Q#GB10):** `pmacs.describe.buffer(b).modified` is
`false` after a generated write. *Bite:* fails against `ad41cf1`,
where it measures `true`.
7. **Both configurations** — default and `--features crdt` — for
criteria 1–4. CRDT must not be the only home of any of them; CI never
enables the feature, and 264 tests are already dark for that reason.
8. **Structural, alongside:** zero `bypass_intercept` writes remain in
`compile.lua` and in `default.lua`'s search panel (comments excepted;
§1.1's arithmetic is the reference).
9. **The three intruder tests still assert what they were written to
assert** after being converted to a Rust-side `read_only` lift
(Q#GB12), rather than being deleted or weakened.
---
## 7. Bets
- **That a per-op `clear_history` is not a throughput problem.** Argued
from `create_undo_manager` being `UndoManager::new(doc)` (O(1) in
document size) and from at most one v0.1 entry existing per clear.
**Measured in Stage 2, not asserted here.**
- **That converting compile's nine sites does not disturb its byte
anchors.** The conversion changes *authority*, not op shape, position
or count — `emit_text`'s `slot.out_pos` arithmetic is untouched. The
bet is that nothing else in the module reads `read_only` indirectly;
criteria 2 and 3 are what test it.
- **That `{ generated = true }` sitting beside `{ bypass_intercept = true }`
is clearer than replacing it.** Q#GB2.
## 8. Deferred (named)
- **The REPL's undo exposure** (Q#GB8), with the §2.5 measurement.
- **Class C: `*buffer-list*`, `*help*`, `*workers*`** (Q#GB9).
- **wdired's unlock** (Q#GB7) — a hard prerequisite recorded onto dired
Stage 3's framing.
- **Suppress-rather-than-clear history recording**, if Stage 2's
measurement says the per-op clear costs anything.
- **`COHERENCE.md` §14's listview consumer list is wrong** (§1.5). Not
edited here; carried in the PR body.
## 9. Coherence impact (`COHERENCE.md` §20)
**Section served: §14 Coherent Workbench Primitives**, and specifically
its **Output channel** bullet, which is where this caveat is already
recorded ("*four writer mechanisms have not yet adopted it and remain
emptiable*"). This arc discharges that entry for Class A and replaces its
"a streaming variant of the primitive that does not exist yet" with one
that does. §14's list-primitive bullet is touched too: listview is called
"the strongest coherence asset in the UI layer", and it is currently
emptiable by one keystroke.
- **Priority 5 (finish the workbench convergence)** is the priority this
serves. It is a correctness debt inside an existing primitive rather
than a new primitive, so it is wiring, not model.
- **§6 interaction islands — none added.** No new keymap scope, no new
dispatch shadow, no new precedence rung. The count stays at six. This
arc deliberately does **not** add undo-chord rebindings anywhere; the
measured point of the bug is that rebinding chords was never the fix.
- **§11 configuration registry — no new settings**, no adoption change.
- **§2 golden journey** — step 6 (compile) and the dired/browse steps are
touched only in the sense that their buffers stop being destructible.
No journey step opens or closes.
- **Background-work attribution — unchanged.** `compile.lua`'s process
pump and the grep stream keep their existing ownership.
- **Protocol — no change.** Nothing new crosses the wire; the fan-out
reuses `queue_daemon_origin_crdt_op`.
- **§14 correction owed:** the listview consumer list (§1.5) and, on
merge, the handoff §4 table, whose four-row inventory is by
`bypass_intercept` and therefore misses Class C.
## 10. Verification plan
Full gate suite per `CLAUDE.md` for **each** PR separately:
```
cargo fmt --check
cargo clippy --workspace --all-targets -- -D warnings # own step
cargo test --lib
cargo test --lib --features crdt
cargo test --test <the touched acceptance suites>
cargo test --test m4_acceptance -- --skip basedpyright
PMACS_REQUIRE_GPU=1 cargo test -p pmacs-gpu
git diff --check
```
Plus, per stage:
- **Stage 1** — `cargo test --test dired_acceptance` and
`--test listview_acceptance`, plus `--test terminal_copy_mode_acceptance`
if Q#GB6 lands, since the cursor clamp changes the shipped snapshot
path.
- **Stage 2** — `cargo test --test compile_mode_acceptance` **and**
`--test compile_mode_crdt_acceptance`, plus
`--test terminal_copy_mode_acceptance` (the `set_generated_contents`
reimplementation and `mark_clean` both reach it). **The search panel
has no suite of its own** — `grep -rln 'search-results' tests/` returns
only `compile_mode_acceptance.rs` and `m4_acceptance.rs`, so Stage 2's
search-panel criteria need a new home rather than an existing one to
extend.
- **Do not gate any new test on `#[cfg(feature = "crdt")]` unless it
genuinely needs CRDT.** CI never enables the feature.
- **Judge the touched suites by elapsed time as well as verdict** where
they reach for a sibling binary (`docs/agent-handoff.md` §5).
- Commit before gating: `cargo fmt` after a commit splits the worktree
from the branch and `git diff --check` will not catch it.
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