M2: the native assembler builds applications

> load Asm.sbx
    > run Say.asm
    wrote Say.sbx: program 46, data 93, labels 7
    > load Say.sbx
    > run built by the machine itself
    it says: built by the machine itself

The machine assembles an application and then runs what it built. Say,
greet and Files all come out byte for byte identical to the C assembler's,
and Tests/native.sh checks all three on every run alongside the boot image
M1 already covered.

WHAT IT TOOK, and it was more than #Include and #Base:

  #Include   The reader is a stack of readers. The current file's whole
             state goes aside - buffer and all, 292 bytes - the new one
             opens, and the end of it pops the old one back. A file goes in
             once; including it twice does nothing, which is what lets two
             libraries depend on a third. The list is forgotten between the
             passes, because the second has to walk the same tree.
  #Base      Cursors start there, so labels hold the addresses the program
             will really have. A program that says where it goes gets the
             SBEX header and a .sbx name; one that says nothing gets SPBT
             and .bin. A program that bases one segment and leaves the
             other unbased with content in it is refused.
  #Reserve   Runs of zeroes, moved over in the first pass and written in
  #Align     the second. How many an #Align comes to depends on where the
             cursor has reached, which is why both passes keep a cursor.
  #Vectors   Names are read and numbered, pinned where the source pins
             them, so SWI osPrintString resolves. Every application needs
             this - a program that calls a service names a vector declared
             in a file it includes.

THE TWO PASSES ARE NOW ONE LOOP, walked twice, with Emitting the only
difference. They have to agree about the length of every token, and the way
they stop agreeing is by being two pieces of code that drifted apart -
which is the exact shape of the bug this assembler found in the C one.
Sharing the body means there is nothing to drift. What is left is checked
anyway: the second pass compares its own totals against the first's and
refuses to write the file if they differ.

THE BUG WORTH RECORDING. The tokenizer holds one character of lookahead,
and at an #Include that character belongs to the file being put aside. It
was carried across and handed back on the way out, which is wrong: a file
runs out in the middle of whatever the tokenizer happens to be doing, so
the character arrives in the middle of a word. `start:` came back as `s`
and then `tart:` - and the result assembled into a perfectly plausible
file. The fix is to undo the read instead, so the character is simply still
there when the file is opened again and the question of when to hand it
back never arises.

Three smaller ones, all old friends: three places took the CONTENTS of a
buffer where they wanted its ADDRESS; vecTakeAuto returned its answer in A,
which a RET puts back; and pass two re-declared every vector because only
the label table was being skipped on the second walk.

sameText moved down into numbers.asm from the label table - four parts want
it now, and a reader test that includes neither labels nor tokens has to
build on its own.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW

SplitBit Assembler Manual.md

@@ -501,8 +501,25 @@ Two passes are enough because **every length is known without resolving anything
 
 One thing is genuinely easier here than on a host. The host assembler searches a list of include directories, because a host has directories; **SBFS is flat**, so an include is a file name and there is nowhere else to look.
 
+### Building Applications:
+
+`#Include` splices another file in where it stands, so the reader is a stack of readers: the current file's whole state goes aside, the new one opens, and the end of it pops the old one back. A file is included **once** — including it twice is not an error, it just does nothing, which is what lets two libraries depend on a third.
+
+`#Base` says where a segment is loaded, and a program that says so gets the SBEX loadable header instead of the SPBT boot one, with a `.sbx` name rather than a `.bin`. `#Reserve` and `#Align` lay down runs of zeroes; how many an `#Align` comes to depends on where the cursor has reached, which is why both passes keep a cursor rather than the second one keeping only a write pointer.
+
+Names in `#Vectors` are read and numbered, pinned where the source pins them, so `SWI osPrintString` resolves. **What a name after `SWI` means is settled by what it follows**, not by anything about the name — the Vector Segment may live in a file included further down and may not have been read yet.
+
+That is everything an application needs:
+
+```
+> load Asm.sbx
+> run Say.asm
+wrote Say.sbx: program 46, data 93, labels 7
+> load Say.sbx
+> run built by the machine itself
+it says: built by the machine itself
+```
+
 ### What It Does Not Do Yet:
 
-`#Include`, `#Base`, `#Align`, `#Reserve` and `#Vectors` are **refused by name** rather than ignored. An assembler that quietly skipped a directive would produce a file that looked right and was the wrong length, which is the worst thing it could do; being told "this assembler does not understand that directive yet" costs nothing and hides nothing.
-
-So what it assembles today is a single file with no includes, which is `Programs/hello.asm` — the oldest program in the repository, and now the first one the machine assembles for itself.
+A `#Vectors` line that names a **handler** rather than only declaring a name. That needs a Vector Segment in the output file and the version two header that carries it, so a program bringing its own interrupt handlers cannot be built on the machine yet. It is refused by name rather than ignored, as everything unfinished here is: an assembler that quietly skipped a directive would produce a file that looked right and was the wrong length, which is the worst thing it could do.