hot-reload attempt (unreviewed, not working)

scripts/pcsx_debug_helper/autoexec.lua

@@ -16,36 +16,60 @@
 -- Companion: scripts/gdb/gdb_tape_atoms.gdb (covers GPRs + atom-aware stepping).
 
 local function register_handlers()
-    if not PCSX.WebServer then PCSX.WebServer = {} end
-    if not PCSX.WebServer.Handlers then PCSX.WebServer.Handlers = {} end
+	if not PCSX.WebServer then PCSX.WebServer = {} end
+	if not PCSX.WebServer.Handlers then PCSX.WebServer.Handlers = {} end
 
-    -- ── GTE state ──
-    PCSX.WebServer.Handlers.gte = function(req)
-        local r = PCSX.getRegisters()
-        local out = { "pc=0x" .. string.format("%x", r.pc) }
-        for i = 0, 31 do
-            out[#out + 1] = string.format("D[%d]=0x%08x C[%d]=0x%08x",
-                i, r.CP2D.r[i], i, r.CP2C.r[i])
-        end
-        return table.concat(out, "\n")
-    end
+	-- ── GTE state ──
+	PCSX.WebServer.Handlers.gte = function(req)
+		local r = PCSX.getRegisters()
+		local out = { "pc=0x" .. string.format("%x", r.pc) }
+		for i = 0, 31 do
+			out[#out + 1] = string.format("D[%d]=0x%08x C[%d]=0x%08x",
+				i, r.CP2D.r[i], i, r.CP2C.r[i])
+		end
+		return table.concat(out, "\n")
+	end
 
-		-- ── GP state (pointer to existing endpoints) ──
-		-- pcsx-redux's Lua GPU API exposes only takeScreenShot(); no GPUSTAT / GP0 / GP1 command log / display state.
-		-- We point to the existing web endpoints that DO expose those (when the emulator is actually rendering. Paused-at-BP frames won't have a fresh frame).
-    PCSX.WebServer.Handlers.gp = function(req)
-        local out = {
-            "gpu_screenshot_png=http://localhost:8080/api/v1/state/still",
-            "vram_raw=http://localhost:8080/api/v1/gpu/vram/raw (1MB VRAM)",
-            "gpustat=NOT_AVAILABLE_VIA_LUA",
-            "gp_command_log=NOT_AVAILABLE_VIA_LUA (use pcsx-redux Debug > GPU Logger)",
-            "hint_run_emulator_unpaused_for_screenshot",
-        }
-        return table.concat(out, "\n")
-    end
+	-- ── GP state (pointer to existing endpoints) ──
+	-- pcsx-redux's Lua GPU API exposes only takeScreenShot(); no GPUSTAT / GP0 / GP1 command log / display state.
+	-- We point to the existing web endpoints that DO expose those (when the emulator is actually rendering. Paused-at-BP frames won't have a fresh frame).
+	PCSX.WebServer.Handlers.gp = function(req)
+		local out = {
+			"gpu_screenshot_png=http://localhost:8080/api/v1/state/still",
+			"vram_raw=http://localhost:8080/api/v1/gpu/vram/raw (1MB VRAM)",
+			"gpustat=NOT_AVAILABLE_VIA_LUA",
+			"gp_command_log=NOT_AVAILABLE_VIA_LUA (use pcsx-redux Debug > GPU Logger)",
+			"hint_run_emulator_unpaused_for_screenshot",
+		}
+		return table.concat(out, "\n")
+	end
 end
 
 local ok, err = pcall(register_handlers)
 if ok then print("[pcsx_debug_helper] handlers registered: gte, gp")
 else       print("[pcsx_debug_helper] registration failed: " .. tostring(err))
 end
+
+-- ── reload handler (Task 6) ──
+-- After gte and gp register successfully, load reload.lua through Support.extra.dofile and call its install(pcsx, support).
+-- The whole sequence runs inside pcall so a missing zip, missing module table,
+-- or throwing install never disturbs the gte and gp handlers already registered above (handler isolation).
+--
+-- The failure messages are intentionally single-line so the helper's boot log stays scannable.
+if    type(Support)              == "table"
+	and type(Support.extra)        == "table"
+	and type(Support.extra.dofile) == "function" then
+	local load_ok, reload_mod = pcall(Support.extra.dofile, "reload.lua")
+	if load_ok and type(reload_mod) == "table" and type(reload_mod.install) == "function" then
+		local install_ok, install_err = pcall(reload_mod.install, PCSX, Support)
+		if install_ok then
+			print("[pcsx_debug_helper] reload handler registered")
+		else
+			print("[pcsx_debug_helper] reload registration failed: " .. tostring(install_err))
+		end
+	else
+		print("[pcsx_debug_helper] reload load failed: " .. tostring(reload_mod))
+	end
+else
+	print("[pcsx_debug_helper] reload load failed: Support.extra.dofile unavailable")
+end

scripts/pcsx_debug_helper/reload.lua

@@ -0,0 +1,902 @@
+-- reload.lua - Side-effect-free hot-reload helper for the
+-- pcsx_redux_hot_reload track (Task 2). This file owns the HTTP request
+-- surface that the launch / reload client targets:
+--
+--   POST /api/v1/lua/reload?mode=prime&target=hello_camera&path=<encoded-elf>
+--   POST /api/v1/lua/reload?mode=elf&target=hello_camera&path=<encoded-elf>
+--   POST /api/v1/lua/reload?mode=patch&target=hello_camera&addr=...&hex=...
+--
+-- This module exposes the public surface used by the contract harness
+-- (tests/reload_helper_contract.lua) and the runtime installed by
+-- scripts/pcsx_debug_helper/autoexec.lua. The module must not reference
+-- the global PCSX table at load time; the host is passed in explicitly
+-- through M.new(host) and M.install(pcsx, support).
+--
+-- Public surface:
+--   M.parse_query(query)         -> table, nil OR nil, err_string
+--   M.json_response(fields)      -> string (sorted keys)
+--   M.parse_manifest(...)        -> Task 3 (real impl uses elf32.lua)
+--   M.new(host)                  -> runtime object (Task 4; stub here)
+--   M.install(pcsx, support)     -> registers web handler (Task 6; stub here)
+--
+-- Companion: scripts/pcsx_debug_helper/autoexec.lua.
+
+-- ---------------------------------------------------------------------------
+-- Load the shared ELF32 helpers.
+--
+-- **The bane of this refactor:** the helper VM (PCSX-Redux) does not expose
+-- `require` for paths outside the helper zip. The production loader is
+-- `Support.extra.dofile("elf32.lua")` — Support.extra.dofile resolves the
+-- name against the helper zip's contents (the zip is generated by the
+-- build script and includes both `reload.lua` and `elf32.lua` after Task 6).
+--
+-- The test harness at `tests/reload_helper_contract.lua` loads `reload.lua`
+-- via standard Lua `dofile` with an absolute path; it does not install a
+-- `Support` object. We detect the runtime context: if `Support.extra.dofile`
+-- exists, use it (production path); otherwise fall back to standard `dofile`
+-- with an absolute path (test harness path).
+-- ---------------------------------------------------------------------------
+local function load_elf32()
+	if type(Support) == "table"
+		and type(Support.extra) == "table"
+		and type(Support.extra.dofile) == "function" then
+		return Support.extra.dofile("elf32.lua")
+	end
+	-- Test harness + any other context that supplies standard Lua dofile.
+	return dofile("C:/projects/Pikuma/ps1/scripts/elf32.lua")
+end
+
+local E = load_elf32()
+
+local M = {}
+
+-- ---------------------------------------------------------------------------
+-- parse_query(query)
+--
+-- Parses an application/x-www-form-urlencoded query string into a table.
+--
+-- Rules (per spec §8 + plan.md Task 2 Step 3):
+--   * Each pair is split on the first '='; the key is to the left, the value
+--     to the right. A pair without '=' is a malformed_pair.
+--   * Percent escapes '%HH' (HH = two hex digits) decode to the corresponding
+--     byte. A '%' not followed by two hex digits is a malformed_escape.
+--   * '+' decodes to a literal space (applied after percent decode).
+--   * A key appearing more than once is a duplicate_key error.
+--
+-- Returns the parsed table on success. On failure returns nil and a stable
+-- error string suitable for the JSON error envelope. An empty / nil query
+-- returns an empty table (not an error).
+-- ---------------------------------------------------------------------------
+local function percent_decode(s)
+	-- Walk the string once, byte by byte. A '%' must be followed by exactly
+	-- two hex digits; '+' decodes to ' '; everything else is passed through.
+	local out = {}
+	local i = 1
+	local len = #s
+	while i <= len do
+		local c = s:sub(i, i)
+		if c == "%" then
+			if i + 2 > len then
+				return nil  -- truncated escape (e.g., '%' at end or '%X')
+			end
+			local hex = s:sub(i + 1, i + 2)
+			local hd1, hd2 = hex:sub(1, 1), hex:sub(2, 2)
+			-- Validate both characters are hex digits.
+			if not (hd1:match("[0-9A-Fa-f]") and hd2:match("[0-9A-Fa-f]")) then
+				return nil  -- malformed escape
+			end
+			out[#out + 1] = string.char(tonumber(hex, 16))
+			i = i + 3
+		else
+			out[#out + 1] = c
+			i = i + 1
+		end
+	end
+	return table.concat(out)
+end
+
+local function plus_to_space(s)
+	-- Standalone helper so callers can decode '+' after percent decoding.
+	return (s:gsub("+", " "))
+end
+
+function M.parse_query(query)
+	if query == nil or query == "" then
+		return {}, nil
+	end
+
+	local result = {}
+	local seen = {}
+
+	for pair in query:gmatch("[^&]+") do
+		-- Split on the first '=' only.
+		local eq = pair:find("=", 1, true)
+		if not eq then
+			return nil, "malformed_pair"
+		end
+		local raw_key   = pair:sub(1, eq - 1)
+		local raw_value = pair:sub(eq + 1)
+
+		-- Percent-decode first, then convert '+' to space. The order matters:
+		-- a '%2B' should decode to '+' (literal plus), not be re-converted to a
+		-- space. Per RFC 1866 §8.2.1, '+' is a literal plus in the encoded form
+		-- only when it represents a space.
+		local key = percent_decode(raw_key)
+		if key == nil then
+			return nil, "malformed_escape"
+		end
+		key = plus_to_space(key)
+
+		local val = percent_decode(raw_value)
+		if val == nil then
+			return nil, "malformed_escape"
+		end
+		val = plus_to_space(val)
+
+		if seen[key] then
+			return nil, "duplicate_key"
+		end
+		seen[key] = true
+
+		result[key] = val
+	end
+
+	return result, nil
+end
+
+-- ---------------------------------------------------------------------------
+-- json_response(fields)
+--
+-- Deterministic JSON object encoder. Returns a string. Keys are sorted
+-- alphabetically before emission so byte-for-byte equality is testable
+-- across runs and across PS1 captures.
+--
+-- Supported value types: string, number, boolean, nil (encoded as null).
+-- Strings escape '\', '"', and the C0 control range (0x00..0x1F). The
+-- named escapes use the conventional single-char forms: \\, \", \b, \f,
+-- \n, \r, \t. Everything else in 0x00..0x1F is \uXXXX.
+-- ---------------------------------------------------------------------------
+local function json_escape_string(s)
+	-- Two passes: first the named escapes, then the catch-all C0 range
+	-- (%c covers 0x00..0x1F in Lua patterns). Using plain string.gsub
+	-- with a literal replacement table covers the named escapes; a
+	-- second gsub handles the rest.
+	s = s:gsub('[\\"]', {
+		["\\"] = "\\\\",
+		['"']  = '\\"',
+	})
+	s = s:gsub("\b", "\\b")
+	s = s:gsub("\f", "\\f")
+	s = s:gsub("\n", "\\n")
+	s = s:gsub("\r", "\\r")
+	s = s:gsub("\t", "\\t")
+	-- Remaining C0 control characters (0x00..0x1F) become \uXXXX. We
+	-- intentionally keep the named escapes above (which are already
+	-- single backslashes in the output) from being re-escaped: gsub on
+	-- the literal control char bytes doesn't match the backslashes we
+	-- already inserted.
+	s = s:gsub("([%c])", function(c)
+		return string.format("\\u%04x", string.byte(c))
+	end)
+	return s
+end
+
+function M.json_response(fields)
+	if type(fields) ~= "table" then
+		error("json_response: expected table, got " .. type(fields))
+	end
+
+	-- Sort keys for deterministic output. Lua's table.sort is byte-wise
+	-- and stable for strings; JSON object key order is not significant
+	-- but tests rely on a fixed order to compare against fixtures.
+	local keys = {}
+	for k in pairs(fields) do
+		keys[#keys + 1] = k
+	end
+	table.sort(keys)
+
+	local parts = {}
+	parts[#parts + 1] = "{"
+	for i = 1, #keys do
+		local k = keys[i]
+		if i > 1 then
+			parts[#parts + 1] = ","
+		end
+		parts[#parts + 1] = '"'
+		parts[#parts + 1] = json_escape_string(k)
+		parts[#parts + 1] = '":'
+		local v = fields[k]
+		local tv = type(v)
+		if tv == "string" then
+			parts[#parts + 1] = '"'
+			parts[#parts + 1] = json_escape_string(v)
+			parts[#parts + 1] = '"'
+		elseif tv == "number" then
+			parts[#parts + 1] = tostring(v)
+		elseif tv == "boolean" then
+			parts[#parts + 1] = v and "true" or "false"
+		elseif v == nil then
+			parts[#parts + 1] = "null"
+		else
+			error("json_response: unsupported value type " .. tv .. " for key " .. tostring(k))
+		end
+	end
+	parts[#parts + 1] = "}"
+	return table.concat(parts)
+end
+
+-- ---------------------------------------------------------------------------
+-- ELF32 manifest parser (Task 3).
+--
+-- Parses a little-endian ELF32 file exposed through a file_adapter that
+-- provides read_u8_at/read_u16_at/read_u32_at/read_size. The parser validates the
+-- magic, class, data encoding, and machine before reading anything else.
+-- It resolves section names through the .shstrtab table and symbols
+-- through every SHT_SYMTAB section (and its linked string table).
+--
+-- The output manifest contains the state ABI the reload gate must
+-- preserve plus the addresses the helper writes to the CPU on a reload.
+-- Loaded sections (SHF_ALLOC, non-SHT_NOBITS) are recorded so the runtime
+-- can reject any ELF whose loaded range overlaps the preserved smem.
+--
+-- **Refactor:** the format-constant tables + the byte-level walker live in
+-- scripts/elf32.lua (loaded above via `load_elf32()`). This module retains
+-- only the manifest-specific validation: required symbols, smem size, stack
+-- alignment, loaded-section overlap. The net effect is ~80 lines shorter.
+--
+-- Stable error codes (returned as the second value):
+--   bad_magic, unsupported_elf_class, unsupported_elf_data,
+--   non_mips_machine, truncated_header, truncated_section_headers,
+--   missing_shstrtab, missing_symtab_strtab, missing_smem,
+--   missing_data_start, missing_data_end, missing_bss_start,
+--   missing_bss_end, missing_stack_top, missing_hot_reload_entry,
+--   zero_smem_size, stack_misaligned, stack_out_of_main_ram,
+--   section_overlaps_smem, bad_file_adapter
+-- ---------------------------------------------------------------------------
+
+-- Convert a KSEG0/KSEG1/physical address to its physical main-RAM offset.
+local function to_physical(addr)
+	if addr >= 0x80000000 and addr < 0x80200000 then
+		return addr - 0x80000000
+	elseif addr >= 0xa0000000 and addr < 0xa0200000 then
+		return addr - 0xa0000000
+	end
+	return addr
+end
+
+-- Strip KSEG0 / KSEG1 alias from an address and return the physical main-RAM
+-- offset. Used by M.elf_reload and M.patch_handler. Returns nil when the
+-- address falls outside physical main RAM (0..0x1fffff), KSEG0 main RAM
+-- (0x80000000..0x801fffff), or KSEG1 main RAM (0xa0000000..0xa01fffff).
+-- Per spec §7 the patch path MUST reject scratchpad (0x1F800000+), BIOS
+-- (0x1FC00000+), MMIO, and expansion aliases; this helper centralizes the
+-- strip + range check so callers cannot forget the upper bound.
+local function strip_kseg(addr)
+	if type(addr) ~= "number" then return nil end
+	if addr >= 0x80000000 and addr < 0x80200000 then
+		return addr - 0x80000000
+	elseif addr >= 0xa0000000 and addr < 0xa0200000 then
+		return addr - 0xa0000000
+	elseif addr >= 0 and addr < 0x200000 then
+		return addr
+	end
+	return nil
+end
+
+-- Parse a hex string ("0xHHHH..." or "HHHH...") into a 32-bit unsigned
+-- integer. Returns nil + stable error on absent / non-hex / out-of-range.
+-- Used for both the patch path's addr/hex query parameters and any other
+-- 32-bit hex field the API may add. Accepts up to 8 hex digits.
+local function parse_hex_u32(s, missing_err, badhex_err)
+	if type(s) ~= "string" or #s == 0 then
+		return nil, missing_err or "missing_hex"
+	end
+	local clean = s:match("^0[xX]([0-9A-Fa-f]+)$")
+		or s:match("^([0-9A-Fa-f]+)$")
+	if not clean then return nil, badhex_err or "non_hex" end
+	if #clean > 8 then return nil, badhex_err or "non_hex" end
+	return tonumber(clean, 16), nil
+end
+
+-- Trap on a missing E.* — keeps the existing one-line-error pattern when
+-- the helper zip is stale or absent.
+local function stack()
+	io.stderr:write("[reload.parse_manifest] FATAL: scripts/elf32.lua not loaded; aborting\n")
+	error("elf32 module not loaded")
+end
+
+local function parse_manifest_impl(file_adapter, target, path, require_entry)
+	-- Wrap the body in a pcall so any thrown exception (e.g. a bad
+	-- adapter method or a malformed section header) surfaces as a
+	-- parse_error with the message and traceback instead of being lost
+	-- into the with_busy_guard xpcall as a generic internal_error.
+	local inner_ok, inner_result, inner_err = pcall(function()
+	-- Validate the adapter surface. E.validate_adapter returns the same
+	-- "bad_file_adapter" error code the prior implementation used.
+	local ok, err = E.validate_adapter(file_adapter)
+	if not ok then return nil, err end
+
+	-- Magic, class, data encoding. E.parse_elf32_headers reads fields at
+	-- the wire offsets specified in E.ELF32_HEADER.
+	local hdr, hdr_err = E.parse_elf32_headers(file_adapter)
+	if not hdr then return nil, hdr_err end
+
+	-- Machine check (e.g. EM_MIPS = 8). e_machine is at offset 0x12 (18).
+	-- The reload helper rejects non-MIPS ELFs before any symbol work.
+	-- Explicit pass style: E.read_u16(adapter, off). The helper wraps the
+	-- Support.File adapter once to strip its implicit `self` so the
+	-- parser shape stays flat-function, not colon-dispatch.
+	local machine = E.read_u16(file_adapter, 0x12)
+	if not machine then return nil, "truncated_header" end
+	if machine ~= E.EM_MIPS then
+		return nil, "non_mips_machine"
+	end
+
+	-- Walk sections. E.walk_sections also resolves .shstrtab names.
+	local sections, walk_err = E.walk_sections(file_adapter, hdr)
+	if not sections then return nil, walk_err end
+
+	-- Walk symbols. E.collect_symbols includes both STB_LOCAL and STB_GLOBAL
+	-- (the live ELF stores smem as a local symbol).
+	local symbols, sym_err = E.collect_symbols(file_adapter, sections)
+	if not symbols then return nil, sym_err end
+
+	-- Required symbols.
+	local smem        = symbols["smem"]
+	local data_start  = symbols["__data_start"]
+	local data_end    = symbols["__data_end"]
+	local bss_start   = symbols["__bss_start"]
+	local bss_end     = symbols["__bss_end"]
+	local stack_top_s = symbols["__sp"]
+	local entry_s     = symbols["hot_reload_entry"]
+
+	if not smem        then return nil, "missing_smem" end
+	if not data_start  then return nil, "missing_data_start" end
+	if not data_end    then return nil, "missing_data_end" end
+	if not bss_start   then return nil, "missing_bss_start" end
+	if not bss_end     then return nil, "missing_bss_end" end
+	if not stack_top_s then return nil, "missing_stack_top" end
+	if require_entry and not entry_s then
+		return nil, "missing_hot_reload_entry"
+	end
+
+	-- Validate smem size.
+	if smem.size == 0 then
+		return nil, "zero_smem_size"
+	end
+
+	-- Validate stack alignment and range.
+	local stack_top = stack_top_s.value
+	if stack_top % 8 ~= 0 then
+		return nil, "stack_misaligned"
+	end
+	local p = to_physical(stack_top)
+	if p < 0 or p > 0x1fffff then
+		return nil, "stack_out_of_main_ram"
+	end
+
+	-- Collect loaded (SHF_ALLOC, non-SHT_NOBITS) sections and check overlap.
+	local loaded = {}
+	local smem_lo = smem.value
+	local smem_hi = smem.value + smem.size
+	for _, s in ipairs(sections) do
+		-- bit 1 (SHF_ALLOC = 0x2) of sh_flags. The modulo-4 trick matches
+		-- the prior implementation; canonicalising on E.SHF_ALLOC would
+		-- gain readability but lose the exact prior behavior.
+		local is_alloc = (s.sh_flags % 4) >= 2
+		if is_alloc and s.sh_type ~= E.SHT_NOBITS and s.sh_size > 0 then
+			loaded[#loaded + 1] = { name = s.name, addr = s.sh_addr, size = s.sh_size }
+			local lo = s.sh_addr
+			local hi = s.sh_addr + s.sh_size
+			if lo < smem_hi and hi > smem_lo then
+				return nil, "section_overlaps_smem"
+			end
+		end
+	end
+
+	return {
+		target             = target,
+		elf_path           = path,
+		elf_entry          = hdr.e_entry,
+		smem_addr          = smem.value,
+		smem_size          = smem.size,
+		bss_start          = bss_start.value,
+		bss_end            = bss_end.value,
+		data_start         = data_start.value,
+		data_end           = data_end.value,
+		hot_reload_entry   = entry_s and entry_s.value or nil,
+		stack_top          = stack_top,
+		loaded_sections    = loaded,
+	}
+	end)
+	if inner_ok then
+		return inner_result, inner_err
+	end
+	-- pcall captured a thrown error; surface as parse_error with the
+	-- message + traceback so the caller can render it.
+	local tb = debug.traceback(inner_result, 2)
+	local err = {
+		parse_error = true,
+		detail = tostring(inner_result),
+		tb = tb,
+	}
+	return nil, err
+end
+
+function M.parse_manifest(file_adapter, target, path, require_entry)
+	if type(E) ~= "table" or type(E.parse_elf32_headers) ~= "function" then
+		stack()
+	end
+	return parse_manifest_impl(file_adapter, target, path, require_entry)
+end
+
+-- ---------------------------------------------------------------------------
+-- Runtime + dispatch (Task 4)
+--
+-- M.new(host) returns a runtime object that owns:
+--   active       -- the most recently primed manifest, or nil
+--   busy         -- boolean guard; only one request runs at a time
+--   host         -- the bound host surface (pause / memory_file / open_file
+--                  / binary_load / invalidate_cache / get_registers)
+--
+-- runtime:handle(req) parses the query through M.parse_query, validates
+-- the mode against a dispatch table, then acquires the busy guard through
+-- xpcall so any error inside the handler releases the guard. The response
+-- is always a JSON string built by M.json_response.
+--
+-- M.prime_active and M.elf_reload are the two handler bodies Task 4 ships.
+-- prime_active always parses with require_entry=false (Phase 0 binary
+-- compatibility). elf_reload always parses with require_entry=true (the
+-- new binary must expose hot_reload_entry). Both validate the parsed
+-- manifest; elf_reload runs the five-field ABI gate before declaring
+-- success. Full host.pause / memory_file / binary_load / invalidate_cache
+-- / get_registers sequencing is Task 5.
+-- ---------------------------------------------------------------------------
+
+-- Convert a manifest into the JSON-serializable field subset. loaded_sections
+-- is excluded because json_response only supports scalars + nil.
+local function manifest_to_response(m)
+	local fields = {
+		ok         = true,
+		target     = m.target,
+		elf_path   = m.elf_path,
+		elf_entry  = m.elf_entry,
+		smem_addr  = m.smem_addr,
+		smem_size  = m.smem_size,
+		bss_start  = m.bss_start,
+		bss_end    = m.bss_end,
+		data_start = m.data_start,
+		data_end   = m.data_end,
+		stack_top  = m.stack_top,
+	}
+	if m.hot_reload_entry then
+		fields.hot_reload_entry = m.hot_reload_entry
+	end
+	return fields
+end
+
+-- Open the new ELF through the host and parse its manifest.
+-- Returns manifest on success; nil + stable error on failure.
+local function parse_manifest_via_host(host, target, path, require_entry)
+	local adapter = host.open_file(path)
+	if not adapter then
+		return nil, "open_file_failed"
+	end
+	return M.parse_manifest(adapter, target, path, require_entry)
+end
+
+-- prime_active: parse with require_entry=false. Accepts Phase 0 binaries
+-- that lack hot_reload_entry. Stores the manifest in runtime.active.
+function M.prime_active(runtime, parsed)
+	local manifest, err = parse_manifest_via_host(
+		runtime.host, parsed.target, parsed.path, false)
+	if not manifest then
+		return M.json_response({ ok = false, error = err, restart_required = true })
+	end
+	runtime.active = manifest
+	return M.json_response(manifest_to_response(manifest))
+end
+
+-- elf_reload: full host-driven reload sequence.
+--
+-- Per conductor/tracks/ps1_pcsx_redux_hot_reload_20260802/spec.md §5 +
+-- plan.md Task 5 Step 4. The canonical 11-entry success log is:
+--
+--   pause, memory_file, state_read, open_new_elf, binary_load,
+--   state_restore, invalidate_cache, get_registers, write_sp,
+--   write_ra, write_pc
+--
+-- Sequencing:
+--
+--   1. Validate the request (target == active.target, path present).
+--   2. Compute the physical address of `active.smem_addr` via
+--      strip_kseg; reject if outside physical main RAM.
+--   3. PARSE PHASE (before pause):
+--        a. elf_handle = host.open_file(parsed.path)
+--        b. manifest = M.parse_manifest(elf_handle, ..., require_entry=true)
+--        c. Run the five-field ABI gate against runtime.active.
+--        d. On any rejection here, return BEFORE pause — the runtime
+--           has invoked host.open_file once (logging "open_file") and
+--           no other host methods.
+--   4. Pause + snapshot:
+--        host.pause()
+--        mem = host.memory_file()
+--        saved = mem:readAtToSlice(active.smem_size, smem_phys)
+--   5. RELOAD PHASE:
+--        elf_handle = host.open_new_elf(parsed.path)  -- second open
+--        loaded = host.binary_load(elf_handle, mem)
+--        if loaded == nil then return binary_load_failed
+--   6. Restore state: mem:writeAtMoveSlice(saved, smem_phys)
+--   7. host.invalidate_cache()
+--   8. Rewrite SP / RA / PC through the FFI register pointer.
+--   9. Replace runtime.active last.
+--  10. Return the JSON envelope.
+--
+-- The two opens are an intentional test-discoverability choice. The
+-- PARSE phase uses host.open_file (it is an existing Task 4 surface
+-- also used by prime); the RELOAD phase uses host.open_new_elf (a
+-- dedicated Task 5 method). In production both methods bind to
+-- Support.File.open so the runtime cost is identical to a single open
+-- — the distinction lives in the test log for ordering verification.
+local function abi_mismatch_response(field, expected, actual)
+	return M.json_response({
+		ok = false, error = "state_abi_mismatch", field = field,
+		expected = expected, actual = actual,
+		restart_required = true,
+	})
+end
+
+function M.elf_reload(runtime, parsed)
+	-- 1. Pre-pause request validation. Pure-Lua, no host calls.
+	if not runtime.active then
+		return M.json_response({
+			ok = false, error = "not_primed", restart_required = false })
+	end
+	if parsed.target ~= runtime.active.target then
+		return M.json_response({
+			ok = false, error = "target_mismatch",
+			expected = runtime.active.target, actual = parsed.target,
+			restart_required = true })
+	end
+	if type(parsed.path) ~= "string" or parsed.path == "" then
+		return M.json_response({
+			ok = false, error = "missing_path",
+			restart_required = false })
+	end
+
+	-- 2. SMEM range check on `active` (the new ELF has not been
+	--    parsed yet; the ABI gate below enforces it cannot relocate).
+	local smem_phys = strip_kseg(runtime.active.smem_addr)
+	if smem_phys == nil or smem_phys < 0 or smem_phys > 0x1fffff then
+		return M.json_response({
+			ok = false, error = "smem_out_of_main_ram",
+			restart_required = true })
+	end
+
+	-- 3. PARSE PHASE — open + parse + ABI gate. On any rejection here,
+	--    only host.open_file has been called. Pause and downstream
+	--    mutations do NOT occur.
+	local elf_handle_for_parse = runtime.host.open_file(parsed.path)
+	if not elf_handle_for_parse then
+		return M.json_response({
+			ok = false, error = "open_file_failed",
+			restart_required = true })
+	end
+	local manifest, parse_err = M.parse_manifest(
+		elf_handle_for_parse, parsed.target, parsed.path, true)
+	if not manifest then
+		return M.json_response({
+			ok = false, error = parse_err,
+			restart_required = true })
+	end
+	local active = runtime.active
+	if manifest.smem_addr ~= active.smem_addr then
+		return abi_mismatch_response(
+			"smem_addr", active.smem_addr, manifest.smem_addr)
+	end
+	if manifest.smem_size ~= active.smem_size then
+		return abi_mismatch_response(
+			"smem_size", active.smem_size, manifest.smem_size)
+	end
+	if manifest.bss_start ~= active.bss_start then
+		return abi_mismatch_response(
+			"bss_start", active.bss_start, manifest.bss_start)
+	end
+	if manifest.bss_end ~= active.bss_end then
+		return abi_mismatch_response(
+			"bss_end", active.bss_end, manifest.bss_end)
+	end
+
+	-- 4. Pause + snapshot smem bytes.
+	runtime.host.pause()
+	local mem = runtime.host.memory_file()
+	local saved = mem:readAtToSlice(active.smem_size, smem_phys)
+
+	-- 5. RELOAD PHASE — second open for binary_load.
+	local elf_handle = runtime.host.open_new_elf(parsed.path)
+	if not elf_handle then
+		return M.json_response({
+			ok = false, error = "open_file_failed",
+			restart_required = true })
+	end
+	local loaded = runtime.host.binary_load(elf_handle, mem)
+	if loaded == nil then
+		-- Do NOT restore state; PCSX.Binary.load may have partially
+		-- written RAM. Keep ACTIVE untouched and tell the caller to
+		-- restart the emulator.
+		return M.json_response({
+			ok = false, error = "binary_load_failed",
+			restart_required = true })
+	end
+
+	-- 6. Restore the smem snapshot over the freshly-loaded code.
+	mem:writeAtMoveSlice(saved, smem_phys)
+
+	-- 7. Flush the CPU instruction cache (.text/.rodata changed).
+	runtime.host.invalidate_cache()
+
+	-- 8. Rewrite SP / RA / PC through the FFI register pointer. The
+	--    PC write must happen last; the CPU starts consuming
+	--    instructions at the new PC the moment the emulator resumes.
+	local regs = runtime.host.get_registers()
+	regs.GPR.n.sp = manifest.stack_top
+	regs.GPR.n.ra = 0
+	regs.pc       = manifest.hot_reload_entry
+
+	-- 9. Replace ACTIVE last so a failed reload cannot poison the
+	--    next request's gate.
+	runtime.active = manifest
+
+	-- 10. Return the JSON envelope.
+	return M.json_response({
+		ok               = true,
+		target           = manifest.target,
+		elf_path         = manifest.elf_path,
+		elf_entry        = manifest.elf_entry,
+		smem_addr        = manifest.smem_addr,
+		smem_size        = manifest.smem_size,
+		bss_start        = manifest.bss_start,
+		bss_end          = manifest.bss_end,
+		data_start       = manifest.data_start,
+		data_end         = manifest.data_end,
+		hot_reload_entry = manifest.hot_reload_entry,
+		stack_top        = manifest.stack_top,
+	})
+end
+
+-- patch_handler: one-word RAM patch through MemoryAsFile.
+--
+-- Per spec §7 + plan.md Task 5 Step 5, the order is:
+--   1. Parse addr and hex query parameters
+--   2. Reject non-hex / missing inputs
+--   3. Reject unaligned addresses (addr & 3)
+--   4. Normalize through strip_kseg; reject out-of-main-RAM
+--      (scratchpad 0x1F800000+, BIOS 0x1FC00000+, MMIO, expansion)
+--   5. host.pause()
+--   6. mem = host.memory_file()
+--   7. mem:writeU32At(value, physical_offset)
+--   8. host.invalidate_cache()
+--   9. Return JSON envelope ok=true with the requested addr and value.
+local function patch_error(err, restart)
+	return M.json_response({
+		ok = false, error = err,
+		restart_required = restart or false,
+	})
+end
+
+function M.patch_handler(runtime, parsed)
+	local addr_str = parsed.addr
+	local hex_str  = parsed.hex
+
+	-- 1. Presence checks.
+	if type(addr_str) ~= "string" or addr_str == "" then
+		return patch_error("missing_addr", false)
+	end
+	if type(hex_str) ~= "string" or hex_str == "" then
+		return patch_error("missing_value", false)
+	end
+
+	-- 2. Hex parse.
+	local addr = parse_hex_u32(addr_str, "missing_addr", "non_hex_addr")
+	if not addr then
+		return patch_error(
+			addr == false and "missing_addr" or "non_hex_addr", false)
+	end
+	local value = parse_hex_u32(hex_str, "missing_value", "non_hex_value")
+	if not value then
+		return patch_error(
+			value == false and "missing_value" or "non_hex_value", false)
+	end
+
+	-- 3. Alignment (checked on the canonical KSEG/physical addr).
+	if addr % 4 ~= 0 then
+		return patch_error("addr_unaligned", false)
+	end
+
+	-- 4. Range check via strip_kseg (rejects KSEG0 > 0x801fffff, KSEG1 >
+	--    0xa01fffff, scratchpad, BIOS, MMIO, expansion, etc.).
+	local phys = strip_kseg(addr)
+	if phys == nil then
+		return patch_error("addr_out_of_main_ram", false)
+	end
+
+	-- 5-8. Pause / write / cache invalidate.
+	runtime.host.pause()
+	local mem = runtime.host.memory_file()
+	mem:writeU32At(value, phys)
+	runtime.host.invalidate_cache()
+
+	-- 9. Return the JSON envelope. Echo the requested address and the
+	-- value in normalized hex so log captures stay stable across runs.
+	return M.json_response({
+		ok    = true,
+		addr  = addr_str,
+		value = "0x" .. string.format("%x", value),
+	})
+end
+
+-- Mode dispatch table. Each handler is invoked with (runtime, parsed).
+-- Tasks 5 adds patch (M.patch_handler); the previous placeholder removed.
+local DISPATCH = {
+	prime = M.prime_active,
+	elf   = M.elf_reload,
+	patch = M.patch_handler,
+}
+
+-- Wrap a handler call with the busy guard. The guard is acquired only
+-- after the mode is validated, so unknown-mode requests do not deadlock
+-- the runtime. xpcall guarantees the guard is released even if the
+-- handler throws.
+local function with_busy_guard(runtime, fn)
+	if runtime.busy then
+		return M.json_response({
+			ok = false, error = "reload_busy", restart_required = false })
+	end
+	runtime.busy = true
+	-- Capture both the error text and a full Lua traceback so the user
+	-- can see the actual failing call site instead of a generic
+	-- "internal_error". debug.traceback("", 2) skips this xpcall frame
+	-- and the json_response frame so the trace starts at the handler.
+	local ok, result = xpcall(fn, function(e)
+		return { msg = tostring(e), tb = debug.traceback("", 2) }
+	end)
+	runtime.busy = false
+	if not ok then
+		return M.json_response({
+			ok = false, error = "internal_error",
+			detail = result.msg, tb = result.tb,
+			restart_required = true })
+	end
+	return result
+end
+
+function M.new(host)
+	if type(host) ~= "table" then
+		error("M.new: host must be a table, got " .. type(host))
+	end
+	local runtime = {
+		active = nil,
+		busy   = false,
+		host   = host,
+	}
+	function runtime:handle(req)
+		-- 1. Parse the query (M.parse_query returns nil, err on failure).
+		local query = req and req.urlData and req.urlData.query or ""
+		local parsed, parse_err = M.parse_query(query)
+		if not parsed then
+			return M.json_response({
+				ok = false, error = parse_err, restart_required = false })
+		end
+		-- 2. Validate the mode against the dispatch table.
+		local mode = parsed.mode
+		local handler = DISPATCH[mode]
+		if not handler then
+			return M.json_response({
+				ok = false, error = "unknown_mode", restart_required = false })
+		end
+		-- 3. Acquire busy and dispatch via xpcall. Mode validation
+		--    happens BEFORE busy is acquired so unknown-mode requests
+		--    cannot deadlock the runtime.
+		return with_busy_guard(self, function()
+			return handler(self, parsed)
+		end)
+	end
+	return runtime
+end
+
+-- Install the reload handler on a PCSX-Redux instance.
+--
+-- Per plan.md Task 5 Step 5 the adapter binds the canonical host method
+-- names to the PCSX-Lua FFI surface:
+--
+--   pause            -> PCSX.pauseEmulator
+--   memory_file      -> PCSX.getMemoryAsFile
+--   open_file        -> Support.File.open(path, "READ")
+--   binary_load      -> PCSX.Binary.load
+--   invalidate_cache -> PCSX.invalidateCache
+--   get_registers    -> PCSX.getRegisters
+--
+-- The returned closure dispatches each request through M.new(host)'s
+-- runtime:handle so the same prime/elf/patch dispatch machinery is used
+-- (including the busy guard from Task 4).
+--
+-- Missing `PCSX.WebServer.Handlers` is created on demand so callers do
+-- not have to wire that themselves; if `PCSX` or `Support` is absent a
+-- single line is printed and the function returns without registering
+-- a handler.
+function M.install(pcsx, support)
+	if type(pcsx) ~= "table" then
+		print("[reload] install failed: PCSX is not a table")
+		return
+	end
+	if type(support) ~= "table"
+		or type(support.File) ~= "table"
+		or type(support.File.open) ~= "function" then
+		print("[reload] install failed: Support.File.open unavailable")
+		return
+	end
+	if type(pcsx.pauseEmulator)   ~= "function" then print("[reload] install failed: PCSX.pauseEmulator missing");   return end
+	if type(pcsx.getMemoryAsFile) ~= "function" then print("[reload] install failed: PCSX.getMemoryAsFile missing"); return end
+	if type(pcsx.Binary)          ~= "table"
+		or type(pcsx.Binary.load)    ~= "function" then print("[reload] install failed: PCSX.Binary.load missing"); return end
+	if type(pcsx.invalidateCache) ~= "function" then print("[reload] install failed: PCSX.invalidateCache missing"); return end
+	if type(pcsx.getRegisters)    ~= "function" then print("[reload] install failed: PCSX.getRegisters missing");    return end
+
+	-- ---------------------------------------------------------------------------
+	-- File adapter wrap.
+	--
+	-- The production pcsx-redux Support.File wrapper (see
+	-- toolchain/pcsx-redux/src/lua/fileffi.lua:225-232 + size() around line 203)
+	-- exposes byte-read methods as colon-syntax closures with camelCase names:
+	--   readU8At  = function(self, pos) ... end
+	--   readU16At = function(self, pos) ... end
+	--   readU32At = function(self, pos) ... end
+	--   size      = function(self) ... end
+	--
+	-- The ELF32 parser (scripts/elf32.lua) uses an explicit-pass shape with
+	-- snake_case names:
+	--   adapter.read_u8_at(off) / adapter.read_u16_at(off) /
+	--   adapter.read_u32_at(off) / adapter.read_size()
+	--
+	-- The install boundary wraps the Support.File return value in a thin
+	-- adapter whose methods forward to the production closures, stripping
+	-- the implicit `self` and re-exporting the names the parser validates.
+	-- Without this wrap, E.validate_adapter returns "bad_file_adapter"
+	-- because adapter.read_u8_at / read_u16_at / read_u32_at / read_size
+	-- are not present on the raw Support.File return.
+	local function wrap_file(f)
+		return {
+			read_u8_at  = function(off) return f:readU8At(off)  end,
+			read_u16_at = function(off) return f:readU16At(off) end,
+			read_u32_at = function(off) return f:readU32At(off) end,
+			read_size   = function()    return f:size()         end,
+		}
+	end
+
+	local host = {
+		pause            = function() pcsx.pauseEmulator() end,
+		memory_file      = function() return pcsx.getMemoryAsFile() end,
+		open_file        = function(path) return wrap_file(support.File.open(path, "READ")) end,
+		-- open_new_elf returns the raw Support.File object because the
+		-- RELOAD phase passes it directly to PCSX.Binary.load which
+		-- expects a real File (with readAt / size), NOT the elf32
+		-- parser adapter (read_u8_at / read_u16_at / read_u32_at /
+		-- read_size). Wrapping it in the adapter here triggers the
+		-- binffi.lua "Expected a File object as first argument" error.
+		open_new_elf     = function(path) return support.File.open(path, "READ") end,
+		binary_load      = function(elf, mem) return pcsx.Binary.load(elf, mem) end,
+		invalidate_cache = function() pcsx.invalidateCache() end,
+		get_registers    = function() return pcsx.getRegisters() end,
+	}
+	local runtime = M.new(host)
+
+	if type(pcsx.WebServer) ~= "table" then pcsx.WebServer = {} end
+	if type(pcsx.WebServer.Handlers) ~= "table" then pcsx.WebServer.Handlers = {} end
+	pcsx.WebServer.Handlers.reload = function(req)
+		return runtime:handle(req)
+	end
+
+	print("[reload] handler installed: reload")
+end
+
+return M