src/add/plan.bend fails

add/plan: ez add as a pure planner. It reads a World (add/world.bend) and returns either the questions it still needs answered (step) or a Plan: the effects to run and how the command ends (plan). The interpreter (add/run.bend) loops on step, answering each question by IO, until nothing is left to ask, then executes the plan.

Before it asks anything the planner refuses what needs no answer: no ledger, one that does not parse, a target that names nothing, a --rename that is no TOML bare key, and a name clash the ledger alone decides (a --rename, or a source it already records). Then it asks at most three rounds: what the ref names (the remote's tags, then its HEAD when no tag is semver-ish; or the named ref), then the checkout at that rev, which carries its NAR hash and the text of every file. A 40-hex ref is the commit, and the first question is the checkout. Every question carries the source as git is to read it, P.anchor(here, url), which the planner computes.

With the checkout answered, the package is walked from its entry by the pure walk (K.of) over the checkout's files, so the hash, the texts laid and the manifest come from one list. The entry is the one given, else the checkout's [package] entry, bin or main.bend, and one the checkout does not hold is refused. The name is Named.as's, refused when Named.why.as objects.

The plan of an add that succeeds, in order: the tree laid under $BEND_LIB, or under .ez/lib when the entry it replaces is vendored; ez.toml written with the dependency added (Rend.add.keep, which keeps that vendor bit); .gitignore written when the allowlist I.sync derives from the new ledger changes it; the old committed tree removed when a vendored dependency's hash moved and nothing else names it; and the lines a person is told. A refusal has no effect at all: nothing laid, nothing written, no cache fill.

A target bend reads as a hub package's <name>@<version> is planned by add/hub.bend instead (H.plan). command is the plan ez add runs, which is plan for a git or path target and H.plan for a name, and next is the interpreter's step over both.

The Effect, Plan and Outcome types are the lock's (lock/plan.bend), as for ez remove and ez init; see "Update (A1, A4)" and "Update (A2)" in docs/rfc/ez-add-planner.md.