Use python3 as the canonical command name course-wide (#104) (#105)

modules/09-issues-and-the-task-layer/README.md

@@ -105,8 +105,8 @@ well-formed version of the same bug:
 
 > **Title:** `done` command crashes on an out-of-range or non-integer index
 >
-> **Context:** `python cli.py done 99` on a list with 3 tasks raises an uncaught `IndexError` and
-> dumps a traceback. `python cli.py done abc` raises `ValueError`. Either way the user sees a stack
+> **Context:** `python3 cli.py done 99` on a list with 3 tasks raises an uncaught `IndexError` and
+> dumps a traceback. `python3 cli.py done abc` raises `ValueError`. Either way the user sees a stack
 > trace instead of a helpful message.
 >
 > **Acceptance criteria:**
@@ -264,7 +264,7 @@ plenty it still can't do. Because it's carried forward across modules, skip anyt
 already built (a `delete` command, task priorities) and pick work that's genuinely still missing.
 Good candidates:
 
-1. **A bug**: `python cli.py done 99` (an out-of-range index) and `python cli.py done abc` (a
+1. **A bug**: `python3 cli.py done 99` (an out-of-range index) and `python3 cli.py done abc` (a
    non-integer) both crash with an uncaught traceback. Run them and watch.
 2. **A small, patterned feature**: an `undone <index>` command that clears a task's done flag,
    mirroring the existing `done` command (it's the inverse).

modules/09-issues-and-the-task-layer/lab/example-issues.md

@@ -18,16 +18,16 @@
 
 ## Context / problem
 
-`python cli.py done 99` on a list with 3 tasks raises an uncaught `IndexError` and dumps a Python
-traceback. `python cli.py done abc` raises `ValueError` the same way. The user sees a stack trace
+`python3 cli.py done 99` on a list with 3 tasks raises an uncaught `IndexError` and dumps a Python
+traceback. `python3 cli.py done abc` raises `ValueError` the same way. The user sees a stack trace
 instead of a helpful message, and the process exits as if it crashed.
 
 Reproduce:
 
 ```
-python cli.py add "first"
-python cli.py done 99      # IndexError traceback
-python cli.py done abc     # ValueError traceback
+python3 cli.py add "first"
+python3 cli.py done 99      # IndexError traceback
+python3 cli.py done abc     # ValueError traceback
 ```
 
 ## Acceptance criteria
@@ -61,7 +61,7 @@ command, which already takes an index and flips a task's state; this is simply i
 
 ## Acceptance criteria
 
-- [ ] `python cli.py undone <index>` clears the done flag on the task at that index and saves.
+- [ ] `python3 cli.py undone <index>` clears the done flag on the task at that index and saves.
 - [ ] `undone` with an out-of-range or non-integer index prints a clear error and exits non-zero
       (same behavior as the fixed `done`, see Issue 1).
 - [ ] `list` after `undone` shows that task as not done (`[ ]`).

modules/09-issues-and-the-task-layer/lab/start/README.md

@@ -15,11 +15,11 @@ This is the running example for **Module 1** (where you feel the copy-paste prob
 ## Run it
 
 ```bash
-python cli.py add "read module 1"
-python cli.py add "set up my editor"
-python cli.py list
-python cli.py done 0
-python cli.py list
+python3 cli.py add "read module 1"
+python3 cli.py add "set up my editor"
+python3 cli.py list
+python3 cli.py done 0
+python3 cli.py list
 ```
 
 Requires Python 3.10+ (it uses `list[Task]` style type hints). No third-party packages.

modules/09-issues-and-the-task-layer/lab/start/cli.py

@@ -1,8 +1,8 @@
 """Tiny command-line front end for the demo task app.
 
 Run it:
-    python cli.py add "write the lesson"
-    python cli.py list
+    python3 cli.py add "write the lesson"
+    python3 cli.py list
 
 State is kept in tasks.json next to this file. It's intentionally minimal; the point of this app
 is to be a realistic-but-small thing you change with an AI, not a product.
@@ -31,7 +31,7 @@ def save(tlist: TaskList) -> None:
 def main(argv: list[str]) -> int:
     tlist = load()
     if not argv:
-        print("usage: python cli.py [add <title> | list | done <index> | count | delete <index>]")
+        print("usage: python3 cli.py [add <title> | list | done <index> | count | delete <index>]")
         return 1
 
     command = argv[0]