docs(amiga): complete AmigaOS 3.1/3.2 developer reference — 172 files across 17 sections

Comprehensive technical documentation covering:
- Hardware: OCS/ECS/AGA custom chip registers, Copper & Blitter deep dives
- Boot sequence: cold boot through startup-sequence
- Binary format: HUNK executable spec, relocation, debug info
- Linking & ABI: .fd files, LVO tables, register calling conventions
- Exec kernel: tasks, interrupts, memory, signals, semaphores
- AmigaDOS: file I/O, FFS/OFS layout, CLI/Shell scripting
- Graphics: planar bitmaps, Copper programming, HAM/EHB modes
- Intuition: screens, windows, IDCMP, BOOPSI
- Devices: trackdisk, SCSI, serial, timer, audio, keyboard
- Libraries: utility, expansion, IFFParse, locale, ARexx
- Networking: bsdsocket API, SANA-II, TCP/IP stack comparison
- Toolchain: GCC, vasm/vlink, SAS/C, NDK, debugging
- Reverse engineering: IDA/Ghidra setup, compiler fingerprints, case studies
- CPU & MMU: 68040/060 emulation libs, PMMU, cache management
- Driver development: SANA-II, Picasso96/RTG, AHI audio

All files include breadcrumb navigation. No local paths or proprietary content.

02_boot_sequence/early_startup.md

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+[← Home](../README.md) · [Boot Sequence](README.md)
+
+# Early Startup Control — Boot Options
+
+## Overview
+
+The **Early Startup Control** (ESC) menu appears when both mouse buttons are held during power-on or reset. It provides boot device selection, display mode override, and emergency recovery options.
+
+---
+
+## Activation
+
+- **Both mouse buttons held** before the boot screen hand animation completes
+- On A1200: hold both buttons during "floppy click" phase
+- Requires Kickstart 2.0+ (not available on 1.3)
+
+---
+
+## Menu Options (OS 3.1)
+
+```
+┌──────────────────────────────────┐
+│     EARLY STARTUP CONTROL        │
+│                                  │
+│  Boot With No Startup-Sequence   │
+│  Boot Standard                   │
+│                                  │
+│  Boot Device:                    │
+│    DF0:  (pri 5)                 │
+│    DH0:  (pri 0)                 │
+│                                  │
+│  Display Mode:                   │
+│    ● PAL   ○ NTSC                │
+│                                  │
+│          [BOOT]                  │
+└──────────────────────────────────┘
+```
+
+---
+
+## Recovery Scenarios
+
+| Scenario | Fix |
+|---|---|
+| Corrupted Startup-Sequence | Boot with No Startup-Sequence, then `ED S:Startup-Sequence` |
+| Wrong display mode (no image) | Hold both buttons → change PAL/NTSC |
+| Boot from floppy instead of HD | Select DF0: as boot device |
+| Assign loops / infinite boot | No Startup-Sequence → fix assigns manually |
+
+---
+
+## References
+
+- RKRM: Early Startup chapter
+- OS 3.1 AmigaGuide: `System/BootMenu`