feat(workflows): unify post-mortem stage chat across attach, restore/replay, and send (#1811)

packages/coding-agent/docs/workflows.md

@@ -416,6 +416,8 @@ When a paused stage is resumed with a message, Atomic lets the stage answer that
 
 Durable `/workflow resume` preserves completed stage metadata, active-stage elapsed time, and graph topology. While an LM stage or task is active, repeated durable checkpoints refresh its accumulated pause-adjusted duration even when its session file does not change. Each new Atomic process that reopens the unfinished session mid-chat starts from the latest saved baseline and uses the same continuation prompt shown above, so repeated process-boundary resumes keep status, graph, stored, and lifecycle duration cumulative without double-counting pauses from earlier process segments. Replayed `ctx.stage`, `ctx.task`, `ctx.chain`, `ctx.parallel`, and child-workflow checkpoints keep their original summaries, timing, session/model metadata, and parallel fanout parentage instead of appearing as freshly flattened replay nodes.
 
+**Post-mortem chat vs. execution resume.** These are distinct operations. *Resuming workflow execution* (`/workflow resume`) is for paused, interrupted, recoverably failed, or unfinished durable work; it may replay checkpoints, continue an incomplete stage, and dispatch remaining DAG work. *Opening a post-mortem chat* reopens one terminal agent stage's retained conversation for follow-up only — it never resumes, retries, rewinds, or otherwise changes workflow execution. Any eligible terminal agent stage with a valid retained session opens as an interactive post-mortem chat regardless of how you reach it: same-process `task`/`tasks`/`chain` stages, completed-workflow inspection, generic `/workflow attach` / `/workflow connect`, restored/replayed durable snapshots after a restart, and `workflow({ action: "send" })`. Explicit `/workflow attach <root-run> <nested-stage>` targets are resolved through the expanded graph and routed to the child run that owns the stage while the overlay remains rooted on the requested graph; the resolved owner is preserved when sibling child workflows reuse the same local stage ID. When a nested stage is reopened after a restart or from another checkout, its session cwd comes from the durable root workflow (resolved workflow cwd first, then original invocation cwd) while stage-control ownership remains with the actual child run. Follow-up turns are appended in place to the stage's retained session (no separate fork), so the agent may still invoke its ordinary tools and cause side effects; only the workflow DAG, run/stage status, results, timings, checkpoints, and topology are immutable. Every host session replacement or shutdown invalidates post-mortem handles, including a session whose lazy reopen is still pending: if creation finishes after the boundary, Atomic disposes the newly created session and rejects the already-submitted prompt before it can execute. A stage stays a **read-only transcript** when it has no valid retained agent session — prompt/HIL and boundary/summary nodes, skipped nodes without a completed conversation, non-terminal handle-less stages (another process may still own the session), and missing/malformed/deleted session files. When a known stage cannot be reopened, the attached chat shows the complete `SESSION UNAVAILABLE` explanation down to the supported 40-column minimum instead of incorrectly labeling an invalid file as an archived transcript. Recoverably failed stages keep their execution-resume semantics and are not silently reopened as post-mortem chat.
+
 Workflow stage sessions and first-party subagent transcripts created inside them are classified as **internal** at creation and excluded from the standard `/resume`, `atomic -r`, `--continue`, and global history surfaces. Fork-context stages and subagents inherit the owning run/stage marker in their initial JSONL header, avoiding a briefly visible ordinary session. They remain resumable and inspectable through the workflow-specific commands and tool actions shown here (`/workflow resume`, `/workflow attach`, `workflow({ action: "status" | "stages" | "stage" | "resume" })`), which read the run/stage store and its `sessionFile` links directly. Passing a stage session's file path to `--session` still opens it explicitly. Classification requires exact `internal: true` plus complete run/stage metadata; malformed legacy markers and ordinary user forks remain in standard history. Legacy workflow sessions created before this marker behavior lack provable ownership and continue to appear until they age out.
 
 Human-in-the-loop prompts from `ctx.ui.input`, `ctx.ui.confirm`, `ctx.ui.select`, `ctx.ui.editor`, and `ctx.ui.custom<T>` appear as awaiting-input nodes in the workflow graph viewer, not as chat modals — use `/workflow connect <run-id>` (or F2), then press Enter on the focused node or click a visible graph node directly to focus and open/attach it for local answers.
@@ -1038,7 +1040,7 @@ Control behavior:
 - `stages` lists stage summaries, including flattened stages from nested `ctx.workflow(...)` imports and `sessionFile`/`transcriptPath` when a stage has a persisted session. Use `statusFilter: "all"` to include completed, failed, skipped, and pending stages.
 - `stage` returns details for one stage by stage id, unique prefix, or stage name, including nested child stages shown in the expanded graph and the persisted `sessionFile` when available. Abbreviated stage IDs printed in graph/control messages use this same unique-prefix resolver; collisions return an ambiguity diagnostic rather than selecting a stage.
 - `transcript` is reference-first with a small preview by default: it returns metadata, transcript paths, and up to 5 recent entries. For targeted lookup, quote the exact `sessionFile`/`transcriptPath` value without changing platform separators (preserve Windows backslashes), search it with `rg` or `grep`, then read only small surrounding ranges. Text results include JSON-escaped `sessionFileJson`/`transcriptPathJson` lines for copy-safe path literals. Pass explicit `tail` or `limit` to override the 5-entry preview; `tail` overrides `limit`; `includeToolOutput` includes captured snapshot tool output in snapshot transcript results.
-- `send` delivery modes are `auto`, `answer`, `prompt`, `steer`, `followUp`, and `resume`. Prompt answers can include `promptId` and can carry answer content in `response`, `text`, or `message`; structured UI prompts usually prefer `response`. Follow-up messaging to completed or failed stages reuses the retained `sessionFile` when available so the conversation resumes from the archived stage transcript instead of starting empty; if no session metadata was retained, Atomic refuses the follow-up rather than silently resetting. Arbitrary `ctx.ui.custom<T>` widget prompts require the interactive workflow graph and return a clear unsupported message when targeted through `send`.
+- `send` delivery modes are `auto`, `answer`, `prompt`, `steer`, `followUp`, and `resume`. Prompt answers can include `promptId` and can carry answer content in `response`, `text`, or `message`; structured UI prompts usually prefer `response`. Follow-up messaging to completed or failed stages reuses the retained `sessionFile` when available so the conversation resumes from the archived stage transcript instead of starting empty; if no session metadata was retained, Atomic refuses the follow-up rather than silently resetting. Explicit `delivery: "resume"` or `delivery: "steer"` against a completed post-mortem stage returns a structured `noop` with guidance to use `followUp` or `prompt`; it never appends the supplied text or mutates workflow execution. Arbitrary `ctx.ui.custom<T>` widget prompts require the interactive workflow graph and return a clear unsupported message when targeted through `send`.
 - `delivery: "auto"` first answers a pending prompt, then resumes paused work, then steers a streaming stage, then queues a follow-up.
 - `pause`, `interrupt`, and `kill` can target one top-level run or `all: true`; `stageId` cannot be combined with `all: true`. Stage-scoped controls can target a visible nested child stage from the expanded graph; Atomic routes the operation to the owning nested run internally.
 - `interrupt` is resumable: it pauses live work when pausable stages exist and keeps the run in live history/status.

packages/workflows/CHANGELOG.md

@@ -6,6 +6,15 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 
 ## [Unreleased]
 
+### Added
+
+- Unified workflow **post-mortem stage chat** across every inspection surface. Any eligible terminal agent stage with a valid retained session now reopens as an interactive follow-up conversation — not only completed-workflow inspection (#1758), but also generic `/workflow attach` / `/workflow connect`, restored/replayed durable snapshots after a process restart, and `workflow({ action: "send" })`. A shared runtime resolver (`ensurePostMortemStageHandle`) validates the retained session is an existing, readable, context-bearing Atomic transcript, then lazily reopens it through a detached, single-flight stage-control handle keyed by the real `{ runId, stageId }` (including nested/expanded child stages). Follow-up turns are appended in place to the retained session and the agent keeps its ordinary tools, while run/stage status, results, timings, checkpoints, replay metadata, and graph topology remain immutable — post-mortem chat can never resume, retry, rewind, pause, or re-dispatch workflow execution. Explicit `workflow send` delivery modes `resume` and `steer` on a completed post-mortem stage return a structured `noop` with follow-up guidance and do not append the supplied text. Stages without a valid retained agent session (prompt/HIL and boundary/summary nodes, skipped nodes, non-terminal handle-less stages, and missing/malformed/deleted session files) keep the existing read-only transcript, and recoverably failed stages retain their execution-resume semantics. `workflow send` now revives such a stage on a registry miss and delivers the message as a conversational follow-up instead of reporting `No live handle for stage.` ([#1811](https://github.com/bastani-inc/atomic/issues/1811))
+
+### Fixed
+
+- Fixed session-boundary races in lazy post-mortem stage-chat attachment so every host session replacement or shutdown (`new`, `resume`, `fork`, `reload`, and `quit`) synchronously invalidates detached handles; a retained-session creation that finishes after the boundary is disposed and its already-submitted prompt is rejected instead of executing in the replacement session or leaking an unowned SDK session.
+- Fixed explicit `/workflow attach <root-run> <nested-stage>` commands to resolve expanded child stages through their owning nested run, preserve that owner through overlay retargeting when sibling child runs reuse the same local stage ID, and retain post-mortem resolver failure reasons so invalid or unavailable sessions render a complete actionable `SESSION UNAVAILABLE` explanation—even at the supported 40-column minimum—instead of a misleading archived-transcript label. Reopened nested terminal stages now restore cwd from their durable root workflow metadata (preferring the resolved workflow cwd, then the original invocation cwd) rather than silently falling back to the current review checkout.
+
 ## [0.9.9] - 2026-07-15
 
 ### Changed

packages/workflows/README.md

@@ -600,7 +600,7 @@ Prompt answer replay is live-memory only. `StageSnapshot.promptAnswerState` repo
 - **`renderCall`** — renders a compact workflow call summary in the chat scroll.
 - **`renderResult`** — renders the result or dispatch banner; live progress continues through the widget and graph viewer. Named workflow runs are background-oriented.
 - **`transcript`** — path-only by default when a transcript file exists: use `status`, `stages`, or `stage` to identify the stage and its `sessionFile`/`transcriptPath`, quote the exact path without changing platform separators (for example, preserve Windows backslashes), then search that file with `rg`/`grep` for targeted terms and read only small surrounding ranges. Default text results include JSON-escaped `sessionFileJson`/`transcriptPathJson` lines for copy-safe path literals plus a `lazyReadPrompt`, with `entries: not inlined` so transcript bodies and tool outputs stay out of model context. Passing explicit `tail` or `limit` opts into a bounded inline preview for quick context checks. If no transcript path is available, the action falls back to a bounded preview of up to 5 recent entries with a `fallbackNote`. A registered live stage handle is used when one exists, even before live messages arrive; otherwise the action falls back to stored stage snapshots. Snapshot entries are ordered chronologically before `tail`/`limit` is applied, with terminal result/error entries kept after tool entries when timestamps are missing or tied. `includeToolOutput` applies only to inlined snapshot previews or no-path fallback previews; live session transcripts may not expose tool output.
-- **`send`** — answers pending primitive/structured stage prompts only when `text`, `response`, or `message` is present; an explicit empty string is a valid answer, while an omitted payload is a no-op. Follow-ups to completed or failed stages reuse retained `sessionFile` metadata when available so the conversation resumes from the archived stage transcript instead of starting empty; if no session metadata was retained, the follow-up is refused instead of silently resetting. Arbitrary `ctx.ui.custom<T>` widget prompts require the interactive workflow graph and return a clear unsupported message when targeted through `send`. `delivery: "auto"` answers pending prompts first, then resumes paused stages, steers streaming stages, or queues a follow-up.
+- **`send`** — answers pending primitive/structured stage prompts only when `text`, `response`, or `message` is present; an explicit empty string is a valid answer, while an omitted payload is a no-op. Follow-ups to eligible terminal agent stages revive an interactive **post-mortem chat** through the shared resolver: on a live-handle miss the stage's retained `sessionFile` is validated (existing, readable, context-bearing) and reopened as a detached, single-flight handle so the message is delivered as a conversational follow-up appended in place — the same path used by `/workflow attach`, restored/replayed durable snapshots, and completed-workflow inspection — without resuming, retrying, or re-dispatching workflow execution. If no valid retained session exists, the follow-up is refused (`No live handle for stage.`) instead of silently resetting or exposing a handle-less non-terminal session. Arbitrary `ctx.ui.custom<T>` widget prompts require the interactive workflow graph and return a clear unsupported message when targeted through `send`. `delivery: "auto"` answers pending prompts first, then resumes paused stages, steers streaming stages, or queues a follow-up.
 - **`reload`** — refreshes workflow resources directly in-process instead of queuing a literal `/workflow reload` chat follow-up.
 
 ### F2 keyboard shortcut

packages/workflows/src/durable/completed-catalog.ts

@@ -1,6 +1,6 @@
-import { readFileSync, statSync } from "node:fs";
 import type { RunSnapshot, StageSnapshot } from "../shared/store-types.js";
 import type { WorkflowInputValues } from "../shared/types.js";
+import { isReopenableSessionTranscript } from "../shared/session-transcript.js";
 import type { DurableWorkflowBackend } from "./backend.js";
 import type {
   DurableCheckpoint,
@@ -15,15 +15,6 @@ export type CompletedWorkflowResolution =
   | { readonly kind: "not_found" }
   | { readonly kind: "stale"; readonly entry: ResumableWorkflowEntry };
 
-interface SessionTranscriptEntry {
-  readonly type?: string;
-  readonly id?: string;
-  readonly timestamp?: string;
-  readonly message?: {
-    readonly role?: string;
-    readonly content?: string | object;
-  };
-}
 
 interface StageDraft {
   readonly replayKey: string;
@@ -109,49 +100,6 @@ function validatedStageTranscript(stage: StageSnapshot): StageSnapshot {
   return withoutSessionFile;
 }
 
-function isReopenableSessionTranscript(path: string): boolean {
-  try {
-    const stats = statSync(path);
-    if (!stats.isFile() || stats.size === 0) return false;
-    const lines = readFileSync(path, "utf8").split("\n").filter((line) => line.trim().length > 0);
-    if (lines.length < 2) return false;
-    const entries: SessionTranscriptEntry[] = [];
-    for (const line of lines) {
-      const parsed = JSON.parse(line) as object;
-      if (typeof parsed !== "object" || parsed === null) return false;
-      entries.push(parsed as SessionTranscriptEntry);
-    }
-    const header = entries[0];
-    return header?.type === "session" && typeof header.id === "string" && entries.some(isUsableContextMessage);
-  } catch {
-    return false;
-  }
-}
-
-function isUsableContextMessage(entry: SessionTranscriptEntry): boolean {
-  return entry.type === "message"
-    && typeof entry.id === "string"
-    && typeof entry.timestamp === "string"
-    && typeof entry.message?.role === "string"
-    && hasUsableMessageContent(entry.message.content);
-}
-
-function hasUsableMessageContent(content: string | object | undefined): boolean {
-  if (typeof content === "string") return content.trim().length > 0;
-  return Array.isArray(content) && content.some(hasUsableContentBlock);
-}
-
-function hasUsableContentBlock(block: object): boolean {
-  if (typeof block !== "object" || block === null) return false;
-  const contentBlock = block as {
-    readonly text?: string;
-    readonly thinking?: string;
-    readonly data?: string;
-    readonly name?: string;
-  };
-  return [contentBlock.text, contentBlock.thinking, contentBlock.data, contentBlock.name]
-    .some((value) => typeof value === "string" && value.trim().length > 0);
-}
 
 function stageSnapshotsFromCheckpoints(
   checkpoints: readonly DurableCheckpoint[],