fix(signals): a source pending on a superseding re-ask keeps its transaction blocked (#3462)

.changeset/superseded-source-blocks.md

@@ -0,0 +1,7 @@
+---
+"@solidjs/signals": patch
+---
+
+A transaction blocked on a memo's flight stays blocked while an upstream re-ask supersedes that flight (#3462).
+
+`transitionComplete` judged a reporter's source by its own flight alone (the self entry in `_pendingSources`). A re-ask upstream retires that entry and leaves the source pending on the new flight instead, so the verdict flipped to "complete" while the source's reader still could not render. The transaction was parked, so nothing re-judged it until a re-entry: repeating `setShow(true)` while the first write was held re-entered it, and the flush committed `Show: true` beside `Panel: hidden`, with the panel catching up seconds later at the chain's landing. The source now blocks while it is pending on anything; the landing folds the transaction in as before (A15), and without the repeated write the frames are unchanged.

packages/signals/docs/INTERNALS-ASYNC-STATE.md

@@ -104,7 +104,7 @@ Semantics of the `(_pendingValue, _overrideValue)` pair for an optimistic node
 - `_contested` — effects whose single value slot was written under this transaction and then overwritten by another live transaction or by mainline (#3322). Effects are not shared state, so a shared effect never merges transactions (memos do, via their `_transition` stamp; `recompute`'s stamp re-entry is memo-only since #3407 — an effect's pass belongs to whatever dirtied it); instead `Effect._valueTransition` records which view produced `_value`, `recompute`, when that owner changes, registers the effect on every owed live transaction, and `finalizePureQueue` re-dirties them **before** its heap run so the re-derive and the effect phase land in the same pass — the other view's value is never published. Exception: a settle that reverts optimism (a non-empty `_optimisticNodes`) re-dirties them **after** `_resolveOptimistic`, with the gated replay — between `commitPendingNodes` and the revert the truth is committed but the overrides still display, and a re-derive there composes the two (the #3164 tear; the reveal wake sits post-revert for the same reason). The slot meanwhile holds the frame already on screen, so nothing new is published early. Rules that fall out: a stale (render) reader with no transaction active is mainline and sees a foreign transaction's staged signal as committed (`read`'s fast path and `readNodeFast` apply `stale && el._transition !== null`, matching the slow path); a value computed mainline needs no protection (mainline publishes what it computes, and a transaction whose writes never touched the effect finds it still correct at commit).
 - `onSettled` and the revert re-derive (#3411): the settle drops the overrides in the commit pass and only _enqueues_ their subscribers (the revert's `insertSubs`, the contested and gated replays, the store clears); the pass after re-derives them, and reads do not pull (`prepareComputed(el, false)`). An unowned `onSettled` callback is a one-shot in the commit pass's user phase, so it read the optimistic source already reverted next to a sync memo of it still holding the optimistic value. The fire waits for the heap to drain instead — while `dirtyQueue` has work it re-enqueues itself (`run` swaps the queue, so the re-enqueue lands in the next pass; `enqueue` keeps the drain alive) — which is what settled means: no derivation outstanding. Forcing the re-derive into the commit pass is not an option: an optimistic write completing in its own flush shows its lane frame (applied by `cleanupCompletedLanes`) before the truth, and the store clears compose a torn shape when their readers re-derive inside finalize (#3164).
 - Finalize re-entry (#3319): `finalizePureQueue` can _enter_ a held transaction partway through — a store commit hook (`bumpDeep` on a node the transaction owns), a boundary `_checkSources` write, or a stamped recompute in its heap — and `initTransition` then adopts the batch being finalized. Two rules keep that consistent. **State:** finalize captures the batch it started with and, if `currentBatch` changed, commits/reverts nothing batch-derived (the entered transaction owns it now); a _completing_ transaction whose ambient batch was separate (the #2916 shape) still settles its own containers, since adoption never touched them. **Effects:** ownership. A run applies with the commit of the transaction that computed its value (`Effect._valueTransition`). The ordinary effect phase runs with `activeTransition` set only in a flush whose finalize entered one, so `runEffect` leaves runs owned by a still-held transaction queued — `_modified` stays set — for the next gate to stash with the owner, while everything computed mainline (the write that caused the flush) applies now. Lanes are exempt by construction: they apply their own effects ahead of their transaction (the optimistic view) and their runner ORs `LANE_RUN` into the `type` it passes; the creation-time immediate run in `effect()` passes it too. The exemption is keyed on the _effect_ still having a lane, not on the runner: after a supersession demotes the cascade (#3331, §1), a `LANE_RUN` runner reaching a now lane-less effect whose value was computed under a still-held transaction leaves it queued like any owned run — otherwise the lane would apply the corrected derivation ahead of the commit that is supposed to reveal it. Known residue: writes staged by a hook _before_ the entry are adopted (held) and, because finalize's heap runs after its hooks, their dependents recompute owner-stamped and park with them; an entry that happens _inside_ that heap can leave an earlier mainline-computed effect applied over an adopted source — narrow, and inherited from adoption rather than from this rule.
-- `transitionComplete`: prunes dead reporters (`reporterBlocksSource`), transition is done when no live reporter still blocks a source whose **own flight is up** and no active-override node is blocked on someone else's async. "Own flight is up" is the source's self entry in its `_pendingSources` (#3375) — not `_error.source`, which a later-pending input overwrites on propagation while the flight is still in the air.
+- `transitionComplete`: prunes dead reporters (`reporterBlocksSource`), transition is done when no live reporter still blocks a source that is **still pending** (a non-empty `_pendingSources`) and no active-override node is blocked on someone else's async. Judged by the set, not `_error.source` (#3375: a later-pending input overwrites it on propagation while the flight is still in the air) and not the self entry alone (#3462: an upstream re-ask that supersedes the source's own flight retires that entry and leaves the source pending on the re-ask — its reader still cannot render, and the landing folds the transaction in; judged complete instead, a re-entry before the landing, such as a repeated write to the held signal, committed the held writes beside the reader's stale frame).
 - Fallback-caught async holds nothing — in both orders (ruled 2026-09-12, #3375). A collecting boundary consumes the notification, so a reader under a fallback never registers. A reader registered while its boundary showed content (forwarded) stays registered when the boundary's `on` changes and it flips to the fallback; `reporterBlocksSource` therefore walks the reporter's `_queue._parent` chain and treats a reporter behind a collecting pending-type boundary (`_collectionType & STATUS_PENDING && !_initialized`) as not live. If nothing outside the boundary consumes the flight, the hold is over; a reader outside it still holds. The reset itself calls `wakeParked()` so the re-judgement happens in the same drain.
 - Wake of parked transactions (`wokenTransitions`): the flush judges only the _active_ transaction; a parked one is re-entered by a stamped node's landing (`settleTransition`), a stamped recompute, or an action resuming. A reporter that stops counting for another reason — its boundary reset (above), or its disposal by ambient work (#3372: `disposeChildren(self)` on a node with `_transition` and `STATUS_PENDING`; a pending reader is always queued as a pending node, so the stamp is reliable) — is none of those: `reporterBlocksSource` would prune it at the next check, but no check comes, and the writes held with it stay staged. Such sites record the transaction (deduped) and schedule; the flush re-enters a woken transaction from the `finally` of a full pass — reached from the park exit and the normal exit alike — and only when idle: no `activeTransition` and `!scheduled`, which at that point means an empty dirty heap, no write since the heap ran (every write re-arms it) and, the finalize having reverted them, no optimistic ambient nodes. Entering adopts the ambient batch, and ambient work present at that instant would be held behind flights it never read; a wake in a pass with work just falls to the next. Entries are popped in a loop until one enters: a wake whose transaction completed by other means is a bare return (`initTransition` on `_done`) and must not strand the ones behind it. The fast drain defers to the full path while a wake is outstanding so such dead entries are still consumed. A wake with other live reporters re-parks; the idle pass is its only cost. Known shape: the ambient write that triggered the reset commits in its own pass and the released hold in the idle pass after it — two effect runs in one synchronous drain (`Sum: 1`, `Sum: 2` at the same clock time in the #3375 pin), never a visible tear.
 - Staged reads enter (A29, #3408): `read()` calls `enterStagedRead` on every selection that returns `_pendingValue` — the fast paths and the slow path — and it enters `el._transition` unless that is null (ambient batch), already active, or the read is a probe (`pendingCheckActive`). The third entry beside `setSignal` on a stamped node and `recompute` of a stamped node; rule text and the `Panel: 1` beside `Count: 0` shape live in the spec. A stale (render) reader never reaches it: the carve-out below serves it the committed value.