G-038 detail: subshell continuity note - piped `subshell <name>` landing interactive

User note recorded: with per-subshell configs (G-008/G-009), piping
`subshell <name>` then going interactive should reasonably land IN that
subshell (quit unwinding to the initial shell). Does not fall out of the
continuity changes automatically - the subshell stack is repl control flow
and unwinds at pipe-EOF under the current nested model. Options recorded:
re-enter captured subshell stack on restart (fights nesting) vs the natural
fit under G-002 non-nested subshells with console targeting (reattach
reopened console to innermost active subshell). Also noted: a -subshell
flag on the shell subcommand as the primary entry (G-032 launcher-args
candidate).

Assisted-by: harness=claude; primary-model=claude-fable-5; api-location=anthropic.com

goals/G-038-piped-session-continuity.md

@@ -58,6 +58,24 @@ The caller-driven restart already identified during G-036 as the clean fix direc
    stamping by internals - the notice line should show the error message itself so the
    user need not race to inspect.
 
+Subshell continuity (user note 2026-07-08, support if practical - not in acceptance):
+once per-subshell configurations exist (G-008/G-009), a user might reasonably run
+`'subshell <somename>' | <punkexe>` and expect the interactive prompt to be IN that
+subshell, with `quit` unwinding to the initial shell. This does NOT fall out of this
+goal's changes automatically: continuity preserves code-interp state, but the subshell
+stack is repl control flow - under the current synchronous nested model the piped
+`subshell` command nests a repl on the same stdin, and pipe-EOF unwinds the whole
+subshell stack before the restart decision is made, so the prompt would land in the top
+shell (with the subshell's interp-side effects intact but the subshell exited). Options:
+(a) within this goal - capture the active subshell stack at EOF and re-enter it on
+restart (fights the nesting model); (b) the natural home - G-002's non-nested subshell
+architecture with console targeting, where pipe-EOF becomes "reattach the reopened
+console to the innermost active subshell" and quit unwinds normally. Record the outcome
+here; if deferred to G-002, this note is the cross-reference. Related idea (separate
+concern, launcher surface): a `-subshell <name>` flag on the `shell` subcommand as the
+primary way to start inside a named subshell (candidate for the G-032 punk::args
+launcher declarations when subshell configs exist).
+
 Risks / interactions:
 - The teardown-mode branching touches exactly the machinery mapped during G-036
   (shellthread worker lifecycle, shellfilter::run tail, thread teardown ordering) - the