Post-2.0 ConPTY idle-gate refinements (deferred from #84-#88)

[darianmiller]

Tracking ticket for refinements consciously deferred while building the ConPTY
injection-safety gate (#84-#88). Each item is independent and optional; captured
here so they are not lost in closed tickets. None blocks 2.0 -- the gate is
correct and verified as shipped.

1. Strict-idle refinement: "input line non-empty since last B" (from ConPTY: OSC 133 shell-integration prompt-state predicate #85/ConPTY idle gate: three-state + fail-safe hardening (follow-up to #85) #87/Idle gate hardening: document load-bearing child-count OR; lock alt-screen 47/1047 (review follow-up to #87) #88).
   Today IDLE is asserted for the whole 133/633 B..C window regardless of whether
   the user has started typing a command. A tighter signal would treat a non-empty
   input line as not-idle. Two data sources, in preference order:

   • OSC 633;E (VS Code integration) carries the current command line verbatim, so
     an empty E == empty prompt -- a clean, exact signal. We already parse and
     ignore 633;E today; this would consume it.
   • "any keystroke forwarded since the last B" as a coarse over-approximation
     (treats typed-then-deleted as still-typed -- the safe direction) for 133-only
     integrations without E.
     Lower value now that unsolicited Auto-CD is retired (Retire the Auto-CD-on-project-switch feature #89); it only sharpens
     user-initiated refusals, where the user already chose the moment.

2. WSL-without-133 blind spot (from Saved commands: suppress injection when a ConPTY foreground app is active #84/ConPTY: OSC 133 shell-integration prompt-state predicate #85/ConPTY idle gate: three-state + fail-safe hardening (follow-up to #85) #87). A line-oriented program running
   inside the WSL VM (a REPL, WSL-hosted Claude Code) is invisible to the Windows
   Job Object (only wsl.exe is Windows-side) and sets no alt-screen, so a WSL tab
   with no 133 markers reads as UNKNOWN. For user-initiated actions (saved
   commands Saved commands: suppress injection when a ConPTY foreground app is active #84, working-dir buttons ConPTY: Project Dir / File Dir buttons inject into the foreground app (gate + line ending) #86) UNKNOWN proceeds, so injection can reach
   that program. Accepted tradeoff (user chose the moment), but candidate
   mitigations to evaluate: document/recommend OSC 133 bash integration in the WSL
   ~/.bashrc (flips the gate to BUSY over the PTY stream), and/or a WSL-side
   foreground-process probe. Full-screen WSL apps (vim) are already caught by
   alt-screen.

3. Non-intrusive busy warning (from Saved commands: suppress injection when a ConPTY foreground app is active #84/ConPTY: Project Dir / File Dir buttons inject into the foreground app (gate + line ending) #86). WarnShellBusy surfaces the refusal
   via ShowMessage, which feeds the text through the VT parser into the live
   screen at the cursor -- so under a running TUI (e.g. Claude Code) the message
   lands mid-frame and overlaps its rendering (cosmetic, self-healing on the app's
   next repaint; no keystrokes reach the app). A tidier version would surface the
   refusal outside the terminal surface: a MessageBeep, or a transient toolbar /
   status flash.

4. Distinguish UNKNOWN vs BUSY in warnings (from Idle gate hardening: document load-bearing child-count OR; lock alt-screen 47/1047 (review follow-up to #87) #88). The three-state gate allows
   a more precise message: BUSY -> "a program is running"; UNKNOWN -> "can't
   confirm the shell is at a prompt". Currently moot -- consumers only warn on
   BUSY (UNKNOWN proceeds) -- but if any future consumer warns on UNKNOWN it
   should use a distinct message rather than reusing the BUSY text.

Acceptance criteria:

• Each item is either implemented or explicitly declined with a rationale (they are independent; partial completion is fine)

[darianmiller]

Items 3 and 4 implemented in v2.0.115.0. Item 3: WarnShellBusy now surfaces the idle-gate refusal via a transient toolbar status label (FLblStatus on FPanelToolbar, auto-cleared by FStatusTimer after ~5s) instead of ShowMessage, which fed the text through the VT parser into the live screen where it overlapped a running TUI frame. No beep, per request. Item 4: WarnShellBusy now takes the TShellIdleState; sisUnknown yields distinct copy (cannot confirm the shell is at a prompt) vs sisBusy (a program is running). Callers still only warn on sisBusy, so the sisUnknown branch is infrastructure for a future UNKNOWN-warning consumer. Item 1 (strict-idle non-empty-input-since-B) declined: low value now that unsolicited Auto-CD is retired (#89); it only sharpens user-initiated refusals where the user already chose the moment. Item 2 declined for the probe (a WSL-side foreground-process probe is fragile, latency-prone and racy); the documentation mitigation (recommend OSC 133 bash integration in the WSL ~/.bashrc) was split into a new follow-up ticket. Resolved in v2.0.115.0.

[darianmiller]

Completed in v2.0.115.0: items 3 and 4 implemented; items 1 and 2 declined with rationale (item 2 documentation split to a follow-up ticket).