feat(shell): add interactive cya shell session (CYA-WP-0007)

Implement the full interactive shell REPL with session persistence,
opt-in capped/redacted shell history, State Hub orientation and
explicit slash-command writes, orchestrator/safety wiring, end-session
learning hooks, weakness hints, docs, and tests.

README.md

@@ -109,6 +109,60 @@ cya --explain-context "explain the changes in the last commit"
 The output includes a structured suggestion, rationale, and (when relevant) a
 clear preview + confirmation prompt. Nothing executes without your explicit yes.
 
+## Interactive Shell Sessions
+
+Start a stateful console session when you want continuity across turns:
+
+```bash
+cya shell
+cya shell --offline --no-hub          # local smoke / air-gapped mode
+cya shell --with-history              # opt in to capped, redacted shell history
+```
+
+Each session writes a user-owned JSONL artifact under:
+
+```text
+~/.config/cya/sessions/<session-id>.jsonl
+```
+
+Useful slash commands:
+
+```text
+/help                         show shell commands
+/explain                      show last turn context, risk, history, hub, hints
+/hub                          show State Hub workstreams and inbox orientation
+/hub log "summary"            post a progress note after confirmation
+/inbox                        show unread State Hub messages
+/export-session               write a redacted JSON session summary
+/learn                        capture Profile 1 reflections now
+/exit                         close the session
+```
+
+Shell history is off by default. `--with-history` or `[shell_history]` config
+includes at most 50 recent lines from `$HISTFILE` or common shell history files,
+redacts secret-like values, and exposes provenance in `/explain`. One-shot
+`cya "..."` requests remain history-free by default.
+
+Example transcript:
+
+```text
+$ cya shell --offline --no-hub
+cya> summarize recent git changes
+... standard orchestrator response ...
+cya> /explain
+... context envelope, memory, shell history status, hub summary, and hints ...
+cya> /export-session
+Exported session summary: ~/.config/cya/sessions/cya-...-summary.json
+cya> /exit
+Session saved: ~/.config/cya/sessions/cya-...jsonl
+```
+
+State Hub writes never happen automatically. `/hub log` and `/inbox read` are
+explicit operator actions; `/hub log` also asks for confirmation.
+
+See `docs/cya-interactive-shell-session-design.md` and
+`docs/cya-shell-operator-session.md` for the full design and operator example.
+
 ## Safety (core product behavior)
 
 - Genuine rule-based assessment is the primary mechanism.