Chapter 18: patches, every change we made to the bot

These are the only changes to the bot's own code. Each one is a small diff of an upstream file, applied at build time (chapter 17), with a comment in the patched code that starts Carried patch (jev):. Each exists because the host (chapter 4) could not fix the problem from outside: the bad decision is made and acted on inside one ap_tick, or sits in one of upstream's static tables, or between two statements of a static function.

Read in order, they are a fairly good story of what it takes to get from Link's bed to the Pegasus Boots:

flowchart TD
  bed["Link's house"] -->|"0001: stop walking back down the stairs"| sword["the sword, from uncle"]
  sword --> ep["Eastern Palace"]
  ep -->|"0003: the anti-fairy circle is not an enemy to walk into"| bk["the big key ($B8)"]
  bk -->|"0013: a big chest needs its big key"| bow["the bow, from the big chest"]
  bow -->|"0004: let the bow shot through"| armos["the Armos Knights"]
  armos --> pendant["the Pendant of Courage"]
  pendant -->|"0005: the green pendant is bit 0x04"| sahas["Sahasrahla"]
  sahas -->|"0006, 0007, 0008: walk up, talk until he gives, close the text"| boots["the Pegasus Boots"]
  boots -->|"0009, 0010, 0031: dash"| book["the Book of Mudora (wired, not yet proven to land)"]

Aside: two of them undo upstream's own last commit. bcb2537 (2020-02-06) made two changes that broke things its author's earlier video had done fine. One left the bot walking back down every intra-room staircase it had just climbed (0001); the other cleared the Y button on the very frame the bot pressed it to shoot an arrow, so the Armos Knights never took one (0004). Upstream had killed them a month earlier, before the line existed.

Aside: the gap after 0016 is not missing patches. From 0030 the patches came from a separate line of work (movement and combat), numbered apart so that two streams of patches could not collide on a number.

Try it. ls this folder, open any patch, and search the patched file for Carried patch (jev). Then build: nix develop -c buck2 build //third-party/c:patched applies all of them, in name order, and fails if any no longer applies.

For the people who maintain it

The patches

Patch	Upstream files	What it changes	Evidence in research/zbanks-alttp.md
0001	`alttp.c`	`bcb2537`'s early return for `$B0 != 0` also caught intra-room stairs, which count their steps in `$B0`; the bot never consumed the targets it climbed past and walked back down.	"The stairs"
0002	`ap_plan.c`	`ap_goal_choose_hook`: a host may make the goal choice. NULL by default, which is upstream exactly. This is where Jev plugs in (chapter 5).	"Jev at the goal choice"
0003	`ap_snes.h`, `ap_map.c`, `ap_plan.c`	Eastern Palace `$B8`: the anti-fairy circle is an invulnerable obstacle, not an enemy to walk into; the room gets a kill-all script in upstream's own table; kill-all no longer gives up the first frame an enemy is out of reach.	"Eastern Palace `$B8`"
0004	`ap_map.c`	`ap_follow_targets` no longer clears the Y that kill-all's bow shot just pressed.	"The Armos Knights"
0005	`ap_req.c`	The green pendant is bit `0x04` of `$7EF374`, as the game and the Randomizer test it; upstream's `0x01` is the red one, which left Sahasrahla unsatisfiable.	"Sahasrahla"
0006	`ap_map.c`, `ap_plan.c`	The bot can walk up to a solid talking NPC (Sahasrahla) and away again. Both exemptions are gated on `SPRITE_ATTR_TALK`, after the first version made an unrelated sprite transparent to the pathfinder at the castle passage door.	"The boots", "The castle passage door"
0007	`ap_plan.c`	A talk lasts until the NPC's text is done and counts only an item actually given, then Link steps off the NPC.	"The boots"
0008	`alttp.c`	An open text box always gets A, even while Link is mid-dash.	"The boots"
0009	`ap_map.c`	A Pegasus Boots dash for `SCRIPT_SEQUENCE`: four new characters (`8`/`2`/`4`/`6`, numpad directions) hold A with a direction, and `ap_follow_targets` no longer clears a dash's A on plain floor.	"The Book of Mudora"
0010	`ap_map.c`, `ap_plan.c`	A goal for the Library's shelf (room `$0107`), its approach point derived from ROM data, gated on the boots. Proven to attach and gate; not yet proven to land the book.	"The Book of Mudora"
0011	`ap_snes.h`	Room `$0123`'s per-room override for sprite `0xBB`/`0x0200` keeps `SPRITE_ATTR_BLKF`, so the pathfinder stops routing through its real hitbox.	"The door D 0x80 stall in room $0123"
0012	`ap_map.c`	In the Dam's block-puzzle room (`$010B`), raw tile `0x27` is a push block, not a hammer peg.	"The Dam Chest push block"
0013	`ap_plan.c`	A big chest's goal is unsatisfiable until its dungeon's big key is held.	"The Eastern Palace big chest"
0014	`ap_map.c`	Room `$0089`'s north door has no floor before its transition, so its approach point is the door's own tile.	"A door with no vestibule ($0089)"
0015	`ap_map.c`	General: a push that jams (`push_timer` running, Link not moving) marks that cell a wall for the rest of the room visit.	"Never push a block into a wall"
0016	`ap_plan.c`	Hyrule Castle routines are done in open mode; any routine whose screen's chests are all open is complete.	"A routine already done, or already claimed, is never offered again"
0030	`ap_map.c`	General form of 0012: indoors, raw tile `0x27` is never a hammer peg, by the game's own rule.	"The hammer swings at bare floor"
0031	`ap_snes.h`, `ap_map.c`	With the boots, a path may cross bonk rocks (tile `0x57`), and the step onto one is a dash.	not yet written up there
0032	`ap_plan.c`	The glove a liftable needs comes from its tile's own `LFT1`/`LFT2` bits, not one hard-coded tile id.	not yet written up there

CLAUDE.md beside this has each patch's full account: the run, the frame, the measurement, and why no host fix could do it.

Path	What
`NNNN-*.patch`	The patches, applied in name order by `//third-party/c:patched`.
README.md	This chapter.
CLAUDE.md	Every patch's evidence, and the open bugs that are not patches yet.

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