[alexandre-vl]

Closes #1000.

Stacked on #1041. Until it merges, this diff includes its code commit; new here are the last two (Claude subagents: forward a foreground subagent's text and thinking and its demo media).

A foreground subagent's tab showed its tool calls and nothing else. Unless asked, Claude Code leaves the text and thinking blocks of a foreground subagent, or of a forked skill, out of the stream. Runs now ask for them, and the adapter folds the thinking blocks they bring.

It needs #1041's spawn gate. Once asked, the CLI forwards subagents "at every nesting depth" (Follow subagent messages). Without the gate, the agents a subagent starts would each open a doc no card lists, and the pill would climb again (1 → 3 in the A/B on #1000).

What changes

• Launch. build_command sets CLAUDE_CODE_FORWARD_SUBAGENT_TEXT=1 (crates/harness/src/claude/mod.rs:349), which "enables the same behavior" as --forward-subagent-text (CLI reference). It's the variable rather than the flag because a CLI older than 2.1.211 ignores the variable, but exits on a flag it doesn't know. A claude started inside the run inherits the variable. Outside stream-json print mode the CLI ignores it "so that nested invocations keep working when it's set process-wide" (environment variables). A nested stream-json claude, such as an Agent SDK script or claude -p --output-format stream-json, forwards its own subagents' text too, which only adds tagged frames to its stream.
• Adapter. A tagged assistant frame's thinking blocks become the subagent's reasoning, in block order with its text and tool calls (crates/harness/src/claude/normalize.rs:728). A signature-only block is skipped, and each thought ends with a blank line, like text blocks. Text blocks were already folded, but they never arrived. A background subagent sends its thinking unasked (live-2.1.228-background-subagent.jsonl, lines 62 and 72), so its tab gains its reasoning too.

Testing

• macOS 27.0, rustc 1.99.0, cargo test --locked: -p zeron-harness --lib --test claude --test codex gives 447, 36 and 45 passed, 3 and 4 ignored as on main. -p zeron-doc --lib and the engine suites give the same counts as on Claude subagents: count and open only this chat's spawns #1041.
• runs_ask_the_cli_to_forward_subagent_text reads the variable off the built command. Without the line it fails with left: None right: Some("1").
• subagent_assistant_blocks_emit_tagged_reasoning_text_and_calls feeds a signature-only thinking block, two thoughts, a text block and a tool call, and expects exactly "Plan it.\n\n", "Then list.\n\n", the text, the call. Folding the empty block, or keeping a thought's trailing space and no blank line, fails it.
• captured_live_forwarded_foreground_subagent_replays_in_order replays frames from Claude Code 2.1.310 run with the variable (live-2.1.310-foreground-subagent-forwarded.jsonl). The subagent's events come out as thinking, "The sky is blue.", echo hi, thinking, "The grass is green.", in that order; without the fold, ["sky", "exec", "grass"]. The capture skips the main thread's 79 frames before its Agent call (28.6 KB, mostly partial deltas), which no assertion reads. One thought that named the account's connectors was reworded.
• captured_live_background_subagent_frames_replay_correctly now also counts the background subagent's two thoughts (2.1.228 capture, lines 62 and 72). Without the fold: left: 0 right: 2.
• Live, Claude Code 2.1.310 with Haiku, the same prompts on the installed v0.2.122, on Claude subagents: count and open only this chat's spawns #1041 and on this branch. The screenshots' v0.2.121 has the same claude driver and sessions.rs: no commit touches them between v0.2.121 and this branch's base.

Subagent tab	v0.2.122 and #1041	This branch
Foreground	the prompt twice, exec	the prompt twice, reasoning, "The sky is blue.", exec, reasoning, "The grass is green."
Background	the prompt, "The sky is blue.", exec, "The grass is green."	the prompt, reasoning, "The sky is blue.", exec, reasoning, "The grass is green."

Only this branch sets the variable, and its background run's journal holds each sentence once: the variable doubles nothing.

• Straight through the CLI with Zeron's flags, a two-agent Workflow run with the variable set sends none of its agents' frames to stdout: 0 tagged frames in 2 runs, as in a run without it. A foreground Agent call in the same setup forwarded its thinking and text. So Claude: open each Workflow agent's live transcript #785, which replays Workflow agents from their transcript files, shows nothing twice.
• Claude subagents: count and open only this chat's spawns #1041's four live prompts, run again on this branch: the pill matched the card's running rows in all 98 samples. The forked /fanout's tab now has the skill's thinking and its reply. The agents it starts forward their text too, and it stays in the run journal (3 and 1 text deltas under their ids, no doc).
• Rebased onto v0.2.124 (c04e3749) after these runs, with no conflict. Merged there with the other five PRs of this series (Claude subagents: count and open only this chat's spawns #1041, Claude subagents: give a typed /skill's fork a chip and a tab #1043, Claude subagents: fill a typed fork's tab while the CLI holds it #1044, Fork: settle the running subagent chips a fork copies #1045, Providers: a switch to turn native subagents off #1046), it passes every suite above again, plus the rest of CI's selection, sync's mock-server tests, zeron-mcp and the UI's settings:: tests, each executable checked to be built from that merge. The one failure, preview's backgrounded_scrubbed_terminal_and_out_of_tree_servers_stay_attributed, fails the same way on v0.2.124 alone, on this Mac.
  • Live on that merged build: the foreground subagent's tab held The sky is blue., the echo call, The grass is green. and two thoughts, and the pill matched the rows in all 14 samples.
• Not run: CLIs older than 2.1.211 (2.1.308 to 2.1.310 are installed), Windows and Linux.

Known limits

• A foreground subagent's tab shows its prompt twice, with or without this. Claude: stop doubling a foreground subagent's opening prompt #952 fixes that.
• A subagent's text arrives as whole blocks, not streamed. Two unedited 2.1.310 captures with the variable set (184 and 314 frames) have 102 and 123 stream_event frames, none of them tagged.
• Per the same docs, forwarding at every depth needs 2.1.219, and a forked skill's text 2.1.265. Older CLIs keep today's tabs.

Screenshots

Offscreen renders of the production Shell (Window::render_to_image), attached to each engine, with the subagent's tab open; docs/media/forward-subagent-text/README.md says how they were made. The media are in their own commit, 20cddd40, if you'd rather drop them before merging.

v0.2.121	This branch

Full windows

v0.2.121	This branch

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[zeronsh]

Security audit clean: Rust and test fixtures only, plus PNG demo media (verified real PNGs). No dependency, build, CI or network changes; the one runtime change sets CLAUDE_CODE_FORWARD_SUBAGENT_TEXT=1 on the claude child. Reviewed the spawn gate (#1041's commit, included here) and the tagged-thinking fold; both look correct. Rebased onto main (98abb77). Locally: harness lib 446, claude 36, codex 45, doc 151, proto 89, engine sessions 22, all passing; clippy and rustfmt add nothing new.