Revision 7 of `docs/destination-capture-framing.md`, closing the
correctness blocker review found in `0efc8c0` and the smaller
reachability hole beside it.
THE BLOCKER. The `"panel"` commit profile skipped preflight checks 2-4
on the claim that a panel result never touches a document window. That
claim is false: panel placement FALLS BACK to an ordinary document
window when the frontend is not `panel_capable` or its one side slot is
dedicated elsewhere -- `apply_placement` says so in its own comment --
and then installs the result there. So a `"panel"` commit could replace
a NEWER document with every stale-intent guard skipped: capture A, the
user opens B, the continuation lands, B is gone. That is the exact
failure `commit_to` exists to prevent, reached through the profile
meant to be the safe one.
WHY NOT A PREFLIGHT PREDICTION. Revision 6 proposed predicting the
fallback at preflight, arguing nothing could change in between because
the body cannot `await`. Refusing `await` prevents another COROUTINE
interleaving; it places no restriction on the body itself, which is
arbitrary Lua running synchronously and can invalidate the snapshot in
two statements -- take the panel, set it `dedicated`, then request a
side display. No preflight predicate closes that, however phrased: the
measurement is taken before the thing it measures is decided.
WHAT THIS DOES INSTEAD. `EditorCore::display_buffer` refuses between
`resolve_placement` and `apply_placement` when a side request resolved
to `PlacementKind::Ordinary` under an active `"panel"` contract whose
destination fails the document preconditions. That is the first moment
the fallback is a fact rather than a guess, and refusing before
`apply_placement` means a refused fallback mutates nothing. The
contract rides on the core, installed and restored by the same
`ScopedFrontendGuard` that scopes the frontend, so a profile can never
outlive the body that declared it; the field is crate-private, so Lua
cannot claim a profile for a placement it did not commit to.
The preflight predicate SURVIVES as an early refusal and not as the
guarantee. `panel_placement_can_fall_back` still gates the relaxation
in `commit_destination_refusal`, so the statically knowable case -- a
frontend that cannot render a panel at all, and will not acquire the
capability mid-body -- refuses before the body allocates a buffer,
registers a handle and paints. That is the same reason `commit_to`
preflights at all. Both layers are pinned, and neither pin subsumes the
other.
The four document checks now live once, in
`EditorCore::document_destination_refusal`: they are evaluated from two
sites, and two hand-written copies is how a backstop ends up weaker
than the thing it backs.
THREE DELIBERATE LIMITS, each a different decision rather than a
stricter version of this one. The document profile is untouched --
re-running its checks at placement would newly refuse dired's own
documented panel path, which is a preservation-suite stop signal. Only
a fallback is guarded, not every `Ordinary` placement -- a `"panel"`
body calling `display_file` is pinned as succeeding. And the refusal is
of the PLACEMENT, not of falling back: a `"panel"` commit with an
intact destination still degrades gracefully into the document window,
because turning graceful degradation into an error would regress every
consumer that works today on a frontend without panel capability.
THE SECOND HOLE. `commit_profile` did `name.to_str()?`, but Lua strings
are BYTE strings, so a `string.char(255)` profile hit mlua's generic
UTF-8 conversion error before `BAD_COMMIT_PROFILE` was ever
constructed -- the same reachability class as the `Option<String>`
defect revision 5 fixed, one layer down. The comparison is on bytes
now, and the invalid-UTF-8 row joins the number/table/boolean rows
asserting on message content.
FOUR DOC SITES repeated the false claim (`ViewDestination`'s own doc
twice, `capture_view_destination`, `ViewDestinationLua`) and are
corrected. Nothing else relied on it: dired, the only Lua `commit_to`
consumer, takes the two-argument document profile and already had all
four checks; `compile.lua`'s `already_in_panel` queries live state; and
the terminal adopter's rollback keys off `created_side`, already false
on a fallback.
Tests: 12 pins, up from 8. Three carry the enforcement split and none
subsumes another -- the pre-established fallback (both causes, the body
must not run), the inside-the-body transition (the body runs, the
result must not land), and the graceful fallback (a valid destination
still lands). Mutation-checked four ways; the pattern of which rows
survive each mutation is in `docs/active-work.md`.
`journey_acceptance` (47) and `dired_acceptance` (31) pass UNCHANGED.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016bqGA6s9tTUFzYpbeW3tai
Levi Neuwirth
86cd08959a