fix(cli): stop status, diff and reconcile hanging on a non-regular destination

CHANGELOG.md

@@ -11,6 +11,41 @@ source layout, CLI surface, and state schema are stabilizing but may still chang
 
 ### Fixed
 
+- **A FIFO at a managed destination no longer hangs `status`, `diff`, `explain`,
+  or `reconcile`'s drift walk and write-back.** (A directory there never hung — `os.ReadFile`
+  fails it immediately with `EISDIR` — and for `status` and `diff` nothing about
+  it changes; only `reconcile`'s write-back now names the shape rather than
+  reporting `EISDIR`.) `os.ReadFile` on a FIFO does
+  not fail — it blocks in the open waiting for a writer that never comes — so
+  the read's own error path never runs and the command never returns. Measured
+  on the previous release: a FIFO at a whole-file destination wedged `diff` and
+  `reconcile`, and a FIFO-shaped key-merge destination (a `~/.claude.json`,
+  say) additionally wedged `status`, which is advertised as read-only. Each had
+  to be killed.
+
+  `status` was already safe for the whole-file shape, because its `hashFile`
+  applied `render.IsRegularOrAbsent` and said it "shares render's predicate so
+  the destination-read guards cannot disagree about what is safe to read". That
+  was true of the hash and false of every other destination read. Every
+  destination read in `internal/cli` — `hashFile` included, which held a second
+  copy of the rule — now goes through one gate, `readDestBytes`, which refuses a
+  non-regular path before the open and lets an ABSENT one through to the read,
+  whose ENOENT is the answer every caller already handles. A `reconcile`
+  write-back (`[w]`) is covered too: with only the classification reads guarded,
+  a non-regular destination would classify as drift and then hang one keystroke
+  later.
+
+  **`apply`, `apply --dry-run`, `reconcile`'s `[o]verride`, `import <agent>` and
+  `doctor` are NOT fixed by this** and still hang on the same fixture — their reads are
+  in `internal/render` and the adapter `Ingest` paths, a far wider sweep.
+  `[o]verride` re-applies through `render.Writer.Write`, so it shares `apply`'s
+  unguarded read; the refusal message therefore points at removing or replacing
+  the file rather than at `[o]`, which would wedge. `doctor` reads no
+  destination itself but reaches one through its plugin check — a FIFO at
+  `~/.claude/settings.json` wedges it after it prints `Plugins`. Tracked as
+  [#241](https://github.com/spxrogers/agentsync/issues/241) and
+  [#242](https://github.com/spxrogers/agentsync/issues/242).
+
 - **`agentsync check` no longer rejects a `[secrets].backend` that `apply`
   accepts.** `secrets.SelectBackend` — the function `apply` actually resolves
   through — lower-cases the backend name, but `check` compared it against the

docs/components.md

@@ -391,7 +391,18 @@ symmetric with the dest→source write boundary (see architecture §7).
   this component KIND reclaimed at all — drives reconcile's prompt wording) and
   `OrphanDeleteWillProceed` (will THIS destination actually be removed on this
   run — keeps the apply summary from counting a skipped delete). `IsRegularOrAbsent`
-  is shared with `internal/cli`'s destination reads so a FIFO cannot block them.
+  is shared with `internal/cli`'s destination reads so a FIFO cannot block
+  **those**: every one of them goes through `readDestBytes`
+  (`internal/cli/destread.go`), which applies this predicate before the open.
+  `TestEveryDestinationReadGoesThroughTheGate` backs this up by failing on a
+  bare `os.ReadFile(op.Path)` anywhere under `internal/cli` — a two-spelling
+  text matcher, so it catches the copy-paste that happened rather than every
+  possible spelling.
+  It is **not** yet true of this package's own `Writer.Write` convergence read
+  or of the adapter `Ingest` paths, so `apply`, `apply --dry-run`,
+  `reconcile --auto-override` (which re-applies through `Writer.Write`),
+  `import <agent>` and `doctor` (through its plugin check) still block on a
+  non-regular destination — issues #241 and #242.
 - **Depends on:** adapter, secrets, source, state, paths, iox, drift.
 - **Files:** `pipeline.go`, `writer.go`, `state_apply.go`, `report.go`.