The plan for wiring the x86 backend to the dev loop, written before the work

docs/handoffs/HANDOFF-x86-devloop.md

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+# Handoff — the x86 backend, wired to the dev loop
+
+Branch `dev-loop`, worktree `agent-aaf84e55296df121c`, from `f459352`. This is items 1, 2 and 3 of
+`HANDOFF-x86-redef.md`'s "What remains": the new-name path, the transient thunk, and the wiring that lets
+`flan dev` choose the backend for a host and its modules together.
+
+**Status: in progress.** This file is written before the work rather than after it, so that a session that ends
+early leaves its plan behind rather than nothing.
+
+## Why
+
+`llc` is 15–17ms of a ~19ms `C-c C-c` (`docs/BUILT.md`). The hand-written backend exists to replace that
+number and has never been given the chance: `--x86` is read only by `flan build`'s argument list, and the
+daemon builds both halves through LLVM. Until it is wired, the backend saves nothing.
+
+## The plan, in the order it will be committed
+
+1. **The new-name path** in `X86.redefinition`. A `slot` predicate beside `fnctx.ext`, a fourth `loc` case
+   for a module-local slot, `flan_dev_cell` / `flan_dev_global` calls in `flan_reload_install`, and an init
+   image for a new global. `test/test_reload.ml`'s v3/v4/v5 fixtures already exist and currently assert a
+   refusal; the transcript replaces it.
+2. **The transient thunk**: `flan_reload_call` and the `@flan_reload_transient` marker, with an x86 analogue
+   of `emit.ml`'s `m.nstr` condition — a module that holds a string literal can never claim to be transient,
+   because the string outlives the call and the agent unloads the mapping.
+3. **The wiring**: an `x86` field on `Session.t` and on `Session.change`, set once in `Dev.start` from
+   `flan dev --x86`, exactly parallel to `debug` — whose own comment already says why both ends have to come
+   from one flag. Never a fallback: if `X86.redefinition` refuses, the daemon reports the refusal. A silent
+   fallback to LLVM is precisely the crossed pair `flan.abi.x86` exists to refuse.
+
+## Decisions, recorded as they are made
+
+(to be filled in)
+
+## Measurements
+
+(to be filled in: emit / assemble / link / dlopen, both backends)