fix(rtk): rtk resolution + absolute-path rewrite — compression was silently dead

rtk lives at ~/.cargo/bin but the hand-managed .bashrc lost the cargo
line: command -v failed in hook AND tool shell, so the hook no-op'd with
a stderr warn on every Bash call — input compression silently OFF.

- Resolve RTK_BIN by probing known install dirs (LRN-036 class).
- Substitute the ABSOLUTE path at the rewrite head: a bare 'rtk …'
  exits 127 in the tool shell, whose PATH the hook cannot fix (proven).
- Compound rewrites carrying further bare rtk segments pass through
  unrewritten: quoted text (commit messages) makes a global substitution
  unsafe — lose compression, never emit a command that 127s (proven:
  a commit chain 127'd mid-flow).
- detect_rtk probes the same dirs so the banner reports capability.
- Re-pinned .rtk-hook.sha256: the rtk BINARY verifies the hook against
  it at execution time and refuses a modified hook — the pin is live
  machinery, not a vestige; coupling documented in the header.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016zA3Qh2Q1QpcGXzXxKeDHR

lib/detect-plugins.sh

@@ -10,7 +10,9 @@
 # --- Always-on plugins ---
 
 detect_rtk() {
-  command -v rtk &>/dev/null
+  command -v rtk &>/dev/null && return 0
+  # PATH heal: hook/session PATH may lack the cargo bin dir (LRN-036 class)
+  [ -x "$HOME/.cargo/bin/rtk" ] || [ -x "$HOME/.local/bin/rtk" ]
 }
 
 detect_superpowers() {