Drop Python 3.9 support, require >=3.10

Author: johnteee

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.9", "3.10", "3.11", "3.12"]
+        python-version: ["3.10", "3.11", "3.12"]
 
     steps:
       - uses: actions/checkout@v6

CHANGELOG.md

@@ -15,7 +15,7 @@ All notable changes to TeaAgent are tracked here.
 - Clarified local developer setup for PEP 668 environments by adding virtualenv-first install steps to `README.md` and `CONTRIBUTING.md`.
 - Updated contributor check commands to use `.venv/bin/...` explicitly for reproducible local lint/type/test runs.
 - Consolidated agent-instruction precedence by making `AGENT.md` a compatibility pointer and declaring `AGENTS.md` as the canonical rule source.
-- Pinned dev `mypy` to `<2` to keep Python 3.9 type-check configuration compatible and avoid local warning churn.
+- Pinned dev `mypy` to `<2` to keep Python 3.10 type-check configuration compatible and avoid local warning churn.
 - Split `teaagent/tui.py` (517 → ~290 lines) by extracting `handle_command` logic to `_commands.py`.
 - Split `teaagent/mcp_http.py` (575 → ~400 lines) by extracting OAuth endpoint handlers to `_oauth.py`.
 - Split `teaagent/telemetry.py` into a `teaagent/telemetry/` package with focused modules: `_availability.py`, `_config.py`, `_audit.py`, `_metrics.py`, and `_transport.py`.

README.md

@@ -47,7 +47,7 @@ Or without the console script:
 python3 -m teaagent.cli --help
 ```
 
-Requires Python >= 3.9. Optional dependency groups enable non-core integrations:
+Requires Python >= 3.10. Optional dependency groups enable non-core integrations:
 
 ```bash
 pip install -e ".[graphqlite]"

docs/adr/0003-p2-code-mode-sandbox.md

@@ -34,7 +34,7 @@ Reject container-level isolation, seccomp, and V8 isolates as P2 scope.
 
 ## Alternatives Considered
 
-- **subinterpreters (PEP 554)**: Not available in Python 3.9; too bleeding-edge.
+- **subinterpreters (PEP 554)**: Not available in Python 3.10; too bleeding-edge (still provisional in 3.12+).
 - **Docker/container per execution**: Latency of ~1s per Code Mode call makes
   it impractical for the dozens of calls an agent may make in one run.
 - **V8/QuickJS isolate via PyMiniRacer or similar**: Adds a C extension dependency