Add stories for the missing compiler driver and interface-expression codegen.

E07-S05 specifies the on-machine n128c driver that prepare-disk and the
compiler launcher already expect; E06-S07 specifies emitting interface
conversions, storage and calls from source. E07-S04 now depends on both, so the
walkthrough cannot be claimed before them.

Generated with Codebuff
Co-Authored-By: Codebuff <noreply@codebuff.com>

newLang/planning/epics-and-stories.md

@@ -555,6 +555,33 @@ compiler/runtime `interfaces.s`, class descriptors, code generation, ABI tests.
   approved debug policy promises detection.
 - `objects.n8` covers multiple interfaces end to end.
 
+### E06-S07 — Interface expressions in code generation (P0)
+
+**Depends on:** E06-S05, E05-S04, E04-S06
+
+**Acceptance criteria:**
+
+- A concrete-to-interface assignment in a statement, argument, return or
+  initializer emits the E06-S04 conversion path and stores all four bytes of
+  the object/table pair; a plain pointer copy is never emitted in its place.
+- `null` in an interface context produces the canonical null interface value,
+  and a call through it takes the documented fault path rather than dispatch.
+- Interface-typed locals, parameters, returns and fields hold and copy the full
+  four bytes, including through array element assignment and struct-style
+  copies.
+- A source-level interface call emits the `if_call` trampoline with the
+  interface value pointer in A/X and the compile-time slot in Y, and passes
+  arguments and receives one- and two-byte returns correctly.
+- A new on-machine fixture with two classes implementing one interface
+  dispatches the same call to different methods, and one class implementing two
+  interfaces dispatches through both, all compiled from source rather than
+  assembled by hand.
+- Misuse stays a stable compile-time diagnostic: assigning an unrelated class
+  to an interface, calling an interface member the interface does not declare,
+  and reaching a private member through an interface each report their
+  catalogued code with no PRG emitted.
+- MAP output names the interface tables and slots the emitted code references.
+
 ---
 
 ## E07 — Vim and Disk Workflow
@@ -600,7 +627,7 @@ integration fixtures, generated `build/` artifacts.
 
 ### E07-S04 — Edit/compile/run walkthrough (P1)
 
-**Depends on:** E07-S03, E06-S06
+**Depends on:** E07-S03, E06-S06, E06-S07, E07-S05
 
 **Acceptance criteria:**
 
@@ -609,6 +636,35 @@ integration fixtures, generated `build/` artifacts.
 - Failure recovery for syntax errors and output collisions is documented.
 - No step requires modifying `vim/` or a reference disk.
 
+### E07-S05 — On-machine compiler driver PRG (P0)
+
+**Depends on:** E07-S01, E04-S01, E04-S06, E02-S04
+
+**Acceptance criteria:**
+
+- `build/n128c.prg` is produced by a documented build script and is the exact
+  file `scripts/prepare-disk.ps1` injects as `n128c` and
+  `scripts/launch-compiler.ps1` autostarts, so the shipped disk and the
+  launcher cannot drift from the driver.
+- Started on `x128` (by hand or through the compiler launcher) the driver takes
+  one source file name, loads it from the session disk through the buffered
+  PETSCII reader with no host-side conversion, runs lexer, parser and code
+  generation, and writes the output PRG named after the source.
+- The driver writes the ERR and MAP outputs for the same run where the
+  corresponding stories produce them, and prints a one-screen summary naming
+  the source, the output, and the diagnostic count.
+- A clean source produces a PRG that runs on `x128`; a source with syntax or
+  semantic errors produces the catalogued diagnostics in the ERR file, a
+  non-zero diagnostic count, and no output PRG.
+- Missing source, unreadable source and an existing output file each end with
+  the documented message and leave the previous output intact rather than a
+  partial file.
+- A test drives the driver through `scripts/launch-compiler.ps1` on a copied
+  development image and checks the PRG, ERR and MAP artifacts and the summary.
+- `docs/editor-workflow.md` documents the command syntax and the recovery steps
+  for a failed compile, and E07-S04's walkthrough can be completed with no
+  undocumented command.
+
 ---
 
 ## E08 — Hardening and Release