audit-context-building/.skillshare-meta.json

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+{
+  "source": "github.com/trailofbits/skills/tree/main/plugins/audit-context-building/skills/audit-context-building",
+  "type": "github-subdir",
+  "installed_at": "2026-01-30T02:23:12.950780406Z",
+  "repo_url": "https://github.com/trailofbits/skills.git",
+  "subdir": "plugins/audit-context-building/skills/audit-context-building",
+  "version": "650f6e3"
+}

audit-context-building/SKILL.md

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+---
+name: audit-context-building
+description: Enables ultra-granular, line-by-line code analysis to build deep architectural context before vulnerability or bug finding.
+---
+
+# Deep Context Builder Skill (Ultra-Granular Pure Context Mode)
+
+## 1. Purpose
+
+This skill governs **how Claude thinks** during the context-building phase of an audit.
+
+When active, Claude will:
+- Perform **line-by-line / block-by-block** code analysis by default.
+- Apply **First Principles**, **5 Whys**, and **5 Hows** at micro scale.
+- Continuously link insights → functions → modules → entire system.
+- Maintain a stable, explicit mental model that evolves with new evidence.
+- Identify invariants, assumptions, flows, and reasoning hazards.
+
+This skill defines a structured analysis format (see Example: Function Micro-Analysis below) and runs **before** the vulnerability-hunting phase.
+
+---
+
+## 2. When to Use This Skill
+
+Use when:
+- Deep comprehension is needed before bug or vulnerability discovery.
+- You want bottom-up understanding instead of high-level guessing.
+- Reducing hallucinations, contradictions, and context loss is critical.
+- Preparing for security auditing, architecture review, or threat modeling.
+
+Do **not** use for:
+- Vulnerability findings
+- Fix recommendations
+- Exploit reasoning
+- Severity/impact rating
+
+---
+
+## 3. How This Skill Behaves
+
+When active, Claude will:
+- Default to **ultra-granular analysis** of each block and line.
+- Apply micro-level First Principles, 5 Whys, and 5 Hows.
+- Build and refine a persistent global mental model.
+- Update earlier assumptions when contradicted ("Earlier I thought X; now Y.").
+- Periodically anchor summaries to maintain stable context.
+- Avoid speculation; express uncertainty explicitly when needed.
+
+Goal: **deep, accurate understanding**, not conclusions.
+
+---
+
+## Rationalizations (Do Not Skip)
+
+| Rationalization | Why It's Wrong | Required Action |
+|-----------------|----------------|-----------------|
+| "I get the gist" | Gist-level understanding misses edge cases | Line-by-line analysis required |
+| "This function is simple" | Simple functions compose into complex bugs | Apply 5 Whys anyway |
+| "I'll remember this invariant" | You won't. Context degrades. | Write it down explicitly |
+| "External call is probably fine" | External = adversarial until proven otherwise | Jump into code or model as hostile |
+| "I can skip this helper" | Helpers contain assumptions that propagate | Trace the full call chain |
+| "This is taking too long" | Rushed context = hallucinated vulnerabilities later | Slow is fast |
+
+---
+
+## 4. Phase 1 — Initial Orientation (Bottom-Up Scan)
+
+Before deep analysis, Claude performs a minimal mapping:
+
+1. Identify major modules/files/contracts.
+2. Note obvious public/external entrypoints.
+3. Identify likely actors (users, owners, relayers, oracles, other contracts).
+4. Identify important storage variables, dicts, state structs, or cells.
+5. Build a preliminary structure without assuming behavior.
+
+This establishes anchors for detailed analysis.
+
+---
+
+## 5. Phase 2 — Ultra-Granular Function Analysis (Default Mode)
+
+Every non-trivial function receives full micro analysis.
+
+### 5.1 Per-Function Microstructure Checklist
+
+For each function:
+
+1. **Purpose**
+   - Why the function exists and its role in the system.
+
+2. **Inputs & Assumptions**
+   - Parameters and implicit inputs (state, sender, env).
+   - Preconditions and constraints.
+
+3. **Outputs & Effects**
+   - Return values.
+   - State/storage writes.
+   - Events/messages.
+   - External interactions.
+
+4. **Block-by-Block / Line-by-Line Analysis**
+   For each logical block:
+   - What it does.
+   - Why it appears here (ordering logic).
+   - What assumptions it relies on.
+   - What invariants it establishes or maintains.
+   - What later logic depends on it.
+
+   Apply per-block:
+   - **First Principles**
+   - **5 Whys**
+   - **5 Hows**
+
+---
+
+### 5.2 Cross-Function & External Flow Analysis
+*(Full Integration of Jump-Into-External-Code Rule)*
+
+When encountering calls, **continue the same micro-first analysis across boundaries.**
+
+#### Internal Calls
+- Jump into the callee immediately.
+- Perform block-by-block analysis of relevant code.
+- Track flow of data, assumptions, and invariants:
+  caller → callee → return → caller.
+- Note if callee logic behaves differently in this specific call context.
+
+#### External Calls — Two Cases
+
+**Case A — External Call to a Contract Whose Code Exists in the Codebase**
+Treat as an internal call:
+- Jump into the target contract/function.
+- Continue block-by-block micro-analysis.
+- Propagate invariants and assumptions seamlessly.
+- Consider edge cases based on the *actual* code, not a black-box guess.
+
+**Case B — External Call Without Available Code (True External / Black Box)**
+Analyze as adversarial:
+- Describe payload/value/gas or parameters sent.
+- Identify assumptions about the target.
+- Consider all outcomes:
+  - revert
+  - incorrect/strange return values
+  - unexpected state changes
+  - misbehavior
+  - reentrancy (if applicable)
+
+#### Continuity Rule
+Treat the entire call chain as **one continuous execution flow**.
+Never reset context.
+All invariants, assumptions, and data dependencies must propagate across calls.
+
+---
+
+### 5.3 Complete Analysis Example
+
+See [FUNCTION_MICRO_ANALYSIS_EXAMPLE.md](resources/FUNCTION_MICRO_ANALYSIS_EXAMPLE.md) for a complete walkthrough demonstrating:
+- Full micro-analysis of a DEX swap function
+- Application of First Principles, 5 Whys, and 5 Hows
+- Block-by-block analysis with invariants and assumptions
+- Cross-function dependency mapping
+- Risk analysis for external interactions
+
+This example demonstrates the level of depth and structure required for all analyzed functions.
+
+---
+
+### 5.4 Output Requirements
+
+When performing ultra-granular analysis, Claude MUST structure output following the format defined in [OUTPUT_REQUIREMENTS.md](resources/OUTPUT_REQUIREMENTS.md).
+
+Key requirements:
+- **Purpose** (2-3 sentences minimum)
+- **Inputs & Assumptions** (all parameters, preconditions, trust assumptions)
+- **Outputs & Effects** (returns, state writes, external calls, events, postconditions)
+- **Block-by-Block Analysis** (What, Why here, Assumptions, First Principles/5 Whys/5 Hows)
+- **Cross-Function Dependencies** (internal calls, external calls with risk analysis, shared state)
+
+Quality thresholds:
+- Minimum 3 invariants per function
+- Minimum 5 assumptions documented
+- Minimum 3 risk considerations for external interactions
+- At least 1 First Principles application
+- At least 3 combined 5 Whys/5 Hows applications
+
+---
+
+### 5.5 Completeness Checklist
+
+Before concluding micro-analysis of a function, verify against the [COMPLETENESS_CHECKLIST.md](resources/COMPLETENESS_CHECKLIST.md):
+
+- **Structural Completeness**: All required sections present (Purpose, Inputs, Outputs, Block-by-Block, Dependencies)
+- **Content Depth**: Minimum thresholds met (invariants, assumptions, risk analysis, First Principles)
+- **Continuity & Integration**: Cross-references, propagated assumptions, invariant couplings
+- **Anti-Hallucination**: Line number citations, no vague statements, evidence-based claims
+
+Analysis is complete when all checklist items are satisfied and no unresolved "unclear" items remain.
+
+---
+
+## 6. Phase 3 — Global System Understanding
+
+After sufficient micro-analysis:
+
+1. **State & Invariant Reconstruction**
+   - Map reads/writes of each state variable.
+   - Derive multi-function and multi-module invariants.
+
+2. **Workflow Reconstruction**
+   - Identify end-to-end flows (deposit, withdraw, lifecycle, upgrades).
+   - Track how state transforms across these flows.
+   - Record assumptions that persist across steps.
+
+3. **Trust Boundary Mapping**
+   - Actor → entrypoint → behavior.
+   - Identify untrusted input paths.
+   - Privilege changes and implicit role expectations.
+
+4. **Complexity & Fragility Clustering**
+   - Functions with many assumptions.
+   - High branching logic.
+   - Multi-step dependencies.
+   - Coupled state changes across modules.
+
+These clusters help guide the vulnerability-hunting phase.
+
+---
+
+## 7. Stability & Consistency Rules
+*(Anti-Hallucination, Anti-Contradiction)*
+
+Claude must:
+
+- **Never reshape evidence to fit earlier assumptions.**
+  When contradicted:
+  - Update the model.
+  - State the correction explicitly.
+
+- **Periodically anchor key facts**
+  Summarize core:
+  - invariants
+  - state relationships
+  - actor roles
+  - workflows
+
+- **Avoid vague guesses**
+  Use:
+  - "Unclear; need to inspect X."
+  instead of:
+  - "It probably…"
+
+- **Cross-reference constantly**
+  Connect new insights to previous state, flows, and invariants to maintain global coherence.
+
+---
+
+## 8. Subagent Usage
+
+Claude may spawn subagents for:
+- Dense or complex functions.
+- Long data-flow or control-flow chains.
+- Cryptographic / mathematical logic.
+- Complex state machines.
+- Multi-module workflow reconstruction.
+
+Subagents must:
+- Follow the same micro-first rules.
+- Return summaries that Claude integrates into its global model.
+
+---
+
+## 9. Relationship to Other Phases
+
+This skill runs **before**:
+- Vulnerability discovery
+- Classification / triage
+- Report writing
+- Impact modeling
+- Exploit reasoning
+
+It exists solely to build:
+- Deep understanding
+- Stable context
+- System-level clarity
+
+---
+
+## 10. Non-Goals
+
+While active, Claude should NOT:
+- Identify vulnerabilities
+- Propose fixes
+- Generate proofs-of-concept
+- Model exploits
+- Assign severity or impact
+
+This is **pure context building** only.

audit-context-building/resources/COMPLETENESS_CHECKLIST.md

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+# Completeness Checklist
+
+Before concluding micro-analysis of a function, verify:
+
+---
+
+## Structural Completeness
+- [ ] Purpose section: 2+ sentences explaining function role
+- [ ] Inputs & Assumptions section: All parameters + implicit inputs documented
+- [ ] Outputs & Effects section: All returns, state writes, external calls, events
+- [ ] Block-by-Block Analysis: Every logical block analyzed (no gaps)
+- [ ] Cross-Function Dependencies: All calls and shared state documented
+
+---
+
+## Content Depth
+- [ ] Identified at least 3 invariants (what must always hold)
+- [ ] Documented at least 5 assumptions (what is assumed true)
+- [ ] Applied First Principles at least once
+- [ ] Applied 5 Whys or 5 Hows at least 3 times total
+- [ ] Risk analysis for all external interactions (reentrancy, malicious contracts, etc.)
+
+---
+
+## Continuity & Integration
+- [ ] Cross-reference with related functions (if internal calls exist, analyze callees)
+- [ ] Propagated assumptions from callers (if this function is called by others)
+- [ ] Identified invariant couplings (how this function's invariants relate to global system)
+- [ ] Tracked data flow across function boundaries (if applicable)
+
+---
+
+## Anti-Hallucination Verification
+- [ ] All claims reference specific line numbers (L45, L98-102, etc.)
+- [ ] No vague statements ("probably", "might", "seems to") - replaced with "unclear; need to check X"
+- [ ] Contradictions resolved (if earlier analysis conflicts with current findings, explicitly updated)
+- [ ] Evidence-based: Every invariant/assumption tied to actual code
+
+---
+
+## Completeness Signal
+
+Analysis is complete when:
+1. All checklist items above are satisfied
+2. No remaining "TODO: analyze X" or "unclear Y" items
+3. Full call chain analyzed (for internal calls, jumped into and analyzed)
+4. All identified risks have mitigation analysis or acknowledged as unresolved

audit-context-building/resources/FUNCTION_MICRO_ANALYSIS_EXAMPLE.md

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+# Function Micro-Analysis Example
+
+This example demonstrates a complete micro-analysis following the Per-Function Microstructure Checklist.
+
+---
+
+## Target: `swap(address tokenIn, address tokenOut, uint256 amountIn, uint256 minAmountOut, uint256 deadline)` in Router.sol
+
+**Purpose:**
+Enables users to swap one token for another through a liquidity pool. Core trading operation in a DEX that:
+- Calculates output amount using constant product formula (x * y = k)
+- Deducts 0.3% protocol fee from input amount
+- Enforces user-specified slippage protection
+- Updates pool reserves to maintain AMM invariant
+- Prevents stale transactions via deadline check
+
+This is a critical financial primitive affecting pool solvency, user fund safety, and protocol fee collection.
+
+---
+
+**Inputs & Assumptions:**
+
+*Parameters:*
+- `tokenIn` (address): Source token to swap from. Assumed untrusted (could be malicious ERC20).
+- `tokenOut` (address): Destination token to receive. Assumed untrusted.
+- `amountIn` (uint256): Amount of tokenIn to swap. User-specified, untrusted input.
+- `minAmountOut` (uint256): Minimum acceptable output. User-specified slippage tolerance.
+- `deadline` (uint256): Unix timestamp. Transaction must execute before this or revert.
+
+*Implicit Inputs:*
+- `msg.sender`: Transaction initiator. Assumed to have approved Router to spend amountIn of tokenIn.
+- `pairs[tokenIn][tokenOut]`: Storage mapping to pool address. Assumed populated during pool creation.
+- `reserves[pair]`: Pool's current token reserves. Assumed synchronized with actual pool balances.
+- `block.timestamp`: Current block time. Assumed honest (no validator manipulation considered here).
+
+*Preconditions:*
+- Pool exists for tokenIn/tokenOut pair (pairs[tokenIn][tokenOut] != address(0))
+- msg.sender has approved Router for at least amountIn of tokenIn
+- msg.sender balance of tokenIn >= amountIn
+- Pool has sufficient liquidity to output at least minAmountOut
+- block.timestamp <= deadline
+
+*Trust Assumptions:*
+- Pool contract correctly maintains reserves
+- ERC20 tokens follow standard behavior (return true on success, revert on failure)
+- No reentrancy from tokenIn/tokenOut during transfers (or handled by nonReentrant modifier)
+
+---
+
+**Outputs & Effects:**
+
+*Returns:*
+- Implicit: amountOut (not returned, but emitted in event)
+
+*State Writes:*
+- `reserves[pair].reserve0` and `reserves[pair].reserve1`: Updated to reflect post-swap balances
+- Pool token balances: Physical token transfers change actual balances
+
+*External Interactions:*
+- `IERC20(tokenIn).transferFrom(msg.sender, pair, amountIn)`: Pulls tokenIn from user to pool
+- `IERC20(tokenOut).transfer(msg.sender, amountOut)`: Sends tokenOut from pool to user
+
+*Events Emitted:*
+- `Swap(msg.sender, tokenIn, tokenOut, amountIn, amountOut, block.timestamp)`
+
+*Postconditions:*
+- `amountOut >= minAmountOut` (slippage protection enforced)
+- Pool reserves updated: `reserve0 * reserve1 >= k_before` (constant product maintained with fee)
+- User received exactly amountOut of tokenOut
+- Pool received exactly amountIn of tokenIn
+- Fee collected: `amountIn * 0.003` remains in pool as liquidity
+
+---
+
+**Block-by-Block Analysis:**
+
+```solidity
+// L90: Deadline validation (modifier: ensure(deadline))
+modifier ensure(uint256 deadline) {
+    require(block.timestamp <= deadline, "Expired");
+    _;
+}
+```
+- **What:** Checks transaction hasn't expired based on user-provided deadline
+- **Why here:** First line of defense; fail fast before any state reads or computation
+- **Assumption:** `block.timestamp` is sufficiently honest (no 900-second manipulation considered)
+- **Depends on:** User setting reasonable deadline (e.g., block.timestamp + 300 seconds)
+- **First Principles:** Time-sensitive operations need expiration to prevent stale execution at unexpected prices
+- **5 Whys:**
+  - Why check deadline? → Prevent stale transactions
+  - Why are stale transactions bad? → Price may have moved significantly
+  - Why not just use slippage protection? → Slippage doesn't prevent execution hours later
+  - Why does timing matter? → Market conditions change, user intent expires
+  - Why user-provided vs fixed? → User decides their time tolerance based on urgency
+
+---
+
+```solidity
+// L92-94: Input validation
+require(amountIn > 0, "Invalid input amount");
+require(minAmountOut > 0, "Invalid minimum output");
+require(tokenIn != tokenOut, "Identical tokens");
+```
+- **What:** Validates basic input sanity (non-zero amounts, different tokens)
+- **Why here:** Second line of defense; cheap checks before expensive operations
+- **Assumption:** Zero amounts indicate user error, not intentional probe
+- **Invariant established:** `amountIn > 0 && minAmountOut > 0 && tokenIn != tokenOut`
+- **First Principles:** Fail fast on invalid input before consuming gas on computation/storage
+- **5 Hows:**
+  - How to ensure valid swap? → Check inputs meet minimum requirements
+  - How to check minimum requirements? → Test amounts > 0 and tokens differ
+  - How to handle violations? → Revert with descriptive error
+  - How to order checks? → Cheapest first (inequality checks before storage reads)
+  - How to communicate failure? → Require statements with clear messages
+
+---
+
+```solidity
+// L98-99: Pool resolution
+address pair = pairs[tokenIn][tokenOut];
+require(pair != address(0), "Pool does not exist");
+```
+- **What:** Looks up liquidity pool address for token pair, validates existence
+- **Why here:** Must identify pool before reading reserves or executing transfers
+- **Assumption:** `pairs` mapping is correctly populated during pool creation; no race conditions
+- **Depends on:** Factory having called createPair(tokenIn, tokenOut) previously
+- **Invariant established:** `pair != 0x0` (valid pool address exists)
+- **Risk:** If pairs mapping is corrupted or pool address is incorrect, funds could be sent to wrong address
+
+---
+
+```solidity
+// L102-103: Reserve reads
+(uint112 reserveIn, uint112 reserveOut) = getReserves(pair, tokenIn, tokenOut);
+require(reserveIn > 0 && reserveOut > 0, "Insufficient liquidity");
+```
+- **What:** Reads current pool reserves for tokenIn and tokenOut, validates pool has liquidity
+- **Why here:** Need current reserves to calculate output amount; must confirm pool is operational
+- **Assumption:** `reserves[pair]` storage is synchronized with actual pool token balances
+- **Invariant established:** `reserveIn > 0 && reserveOut > 0` (pool is liquid)
+- **Depends on:** Sync mechanism keeping reserves accurate (called after transfers/swaps)
+- **5 Whys:**
+  - Why read reserves? → Need current pool state for price calculation
+  - Why must reserves be > 0? → Division by zero in formula if empty
+  - Why check liquidity here? → Cheaper to fail now than after transferFrom
+  - Why not just try the swap? → Better UX with specific error message
+  - Why trust reserves storage? → Alternative is querying balances (expensive)
+
+---
+
+```solidity
+// L108-109: Fee application
+uint256 amountInWithFee = amountIn * 997;
+uint256 numerator = amountInWithFee * reserveOut;
+```
+- **What:** Applies 0.3% protocol fee by multiplying amountIn by 997 (instead of deducting 3)
+- **Why here:** Fee must be applied before price calculation to affect output amount
+- **Assumption:** 997/1000 = 0.997 = (1 - 0.003) represents 0.3% fee deduction
+- **Invariant maintained:** `amountInWithFee = amountIn * 0.997` (3/1000 fee taken)
+- **First Principles:** Fees modify effective input, reducing output proportionally
+- **5 Whys:**
+  - Why multiply by 997? → Gas optimization: avoids separate subtraction step
+  - Why not amountIn * 0.997? → Solidity doesn't support floating point
+  - Why 0.3% fee? → Protocol parameter (Uniswap V2 standard, commonly copied)
+  - Why apply before calculation? → Fee reduces input amount, must affect price
+  - Why not apply after? → Would incorrectly calculate output at full amountIn
+
+---
+
+```solidity
+// L110-111: Output calculation (constant product formula)
+uint256 denominator = (reserveIn * 1000) + amountInWithFee;
+uint256 amountOut = numerator / denominator;
+```
+- **What:** Calculates output amount using AMM constant product formula: `Δy = (x * Δx_fee) / (y + Δx_fee)`
+- **Why here:** After fee application; core pricing logic of the AMM
+- **Assumption:** `k = reserveIn * reserveOut` is the invariant to maintain (with fee adding to k)
+- **Invariant formula:** `(reserveIn + amountIn) * (reserveOut - amountOut) >= reserveIn * reserveOut`
+- **First Principles:** Constant product AMM maintains `x * y = k` (with fee slightly increasing k)
+- **5 Whys:**
+  - Why this formula? → Constant product market maker (x * y = k)
+  - Why not linear pricing? → Would drain pool at constant price (exploitable)
+  - Why multiply reserveIn by 1000? → Match denominator scale with numerator (997 * 1000)
+  - Why divide? → Solving for Δy in: (x + Δx_fee) * (y - Δy) = k
+  - Why this maintains k? → New product = (reserveIn + amountIn*0.997) * (reserveOut - amountOut) ≈ k * 1.003
+- **Mathematical verification:**
+  - Given: `k = reserveIn * reserveOut`
+  - New reserves: `reserveIn' = reserveIn + amountIn`, `reserveOut' = reserveOut - amountOut`
+  - With fee: `amountInWithFee = amountIn * 0.997`
+  - Solving `(reserveIn + amountIn) * (reserveOut - amountOut) = k`:
+    - `reserveOut - amountOut = k / (reserveIn + amountIn)`
+    - `amountOut = reserveOut - k / (reserveIn + amountIn)`
+    - Substituting and simplifying yields the formula above
+
+---
+
+```solidity
+// L115: Slippage protection enforcement
+require(amountOut >= minAmountOut, "Slippage exceeded");
+```
+- **What:** Validates calculated output meets user's minimum acceptable amount
+- **Why here:** After calculation, before any state changes or transfers (fail fast if insufficient)
+- **Assumption:** User calculated minAmountOut correctly based on acceptable slippage tolerance
+- **Invariant enforced:** `amountOut >= minAmountOut` (user-defined slippage limit)
+- **First Principles:** User must explicitly consent to price via slippage tolerance; prevents sandwich attacks
+- **5 Whys:**
+  - Why check minAmountOut? → Protect user from excessive slippage
+  - Why is slippage protection critical? → Prevents sandwich attacks and MEV extraction
+  - Why user-specified? → Different users have different risk tolerances
+  - Why fail here vs warn? → Financial safety: user should not receive less than intended
+  - Why before transfers? → Cheaper to revert now than after expensive external calls
+- **Attack scenario prevented:**
+  - Attacker front-runs with large buy → price increases
+  - Victim's swap would execute at worse price
+  - This check causes victim's transaction to revert instead
+  - Attacker cannot profit from sandwich
+
+---
+
+```solidity
+// L118: Input token transfer (pull pattern)
+IERC20(tokenIn).transferFrom(msg.sender, pair, amountIn);
+```
+- **What:** Pulls tokenIn from user to liquidity pool
+- **Why here:** After all validations pass; begins state-changing operations (point of no return)
+- **Assumption:** User has approved Router for at least amountIn; tokenIn is standard ERC20
+- **Depends on:** Prior approval: `tokenIn.approve(router, amountIn)` called by user
+- **Risk considerations:**
+  - If tokenIn is malicious: could revert (DoS), consume excessive gas, or attempt reentrancy
+  - If tokenIn has transfer fee: actual amount received < amountIn (breaks invariant)
+  - If tokenIn is pausable: could revert if paused
+  - Reentrancy: If tokenIn has callback, attacker could call Router again (mitigated by nonReentrant modifier)
+- **First Principles:** Pull pattern (transferFrom) is safer than users sending first (push) - Router controls timing
+- **5 Hows:**
+  - How to get tokenIn? → Pull from user via transferFrom
+  - How to ensure Router can pull? → User must have approved Router
+  - How to specify destination? → Send directly to pair (gas optimization: no router intermediate storage)
+  - How to handle failures? → transferFrom reverts on failure (ERC20 standard)
+  - How to prevent reentrancy? → nonReentrant modifier (assumed present)
+
+---
+
+```solidity
+// L122: Output token transfer (push pattern)
+IERC20(tokenOut).transfer(msg.sender, amountOut);
+```
+- **What:** Sends calculated amountOut of tokenOut from pool to user
+- **Why here:** After input transfer succeeds; completes the swap atomically
+- **Assumption:** Pool has at least amountOut of tokenOut; tokenOut is standard ERC20
+- **Invariant maintained:** User receives exact amountOut (no more, no less)
+- **Risk considerations:**
+  - If tokenOut is malicious: could revert (DoS), but user selected this token pair
+  - If tokenOut has transfer hook: could attempt reentrancy (mitigated by nonReentrant)
+  - If transfer fails: entire transaction reverts (atomic swap)
+- **CEI pattern:** Not strictly followed (Check-Effects-Interactions) - both transfers are interactions
+  - Typically Effects (reserve update) should precede Interactions (transfers)
+  - Here, transfers happen before reserve update (see next block)
+  - Justification: nonReentrant modifier prevents exploitation
+- **5 Whys:**
+  - Why transfer to msg.sender? → User initiated swap, they receive output
+  - Why not to an arbitrary recipient? → Simplicity; extensions can add recipient parameter
+  - Why this amount exactly? → amountOut calculated from constant product formula
+  - Why after input transfer? → Ensures atomicity: both succeed or both fail
+  - Why trust pool has balance? → Pool's job to maintain reserves; if insufficient, transfer reverts
+
+---
+
+```solidity
+// L125-126: Reserve synchronization
+reserves[pair].reserve0 = uint112(reserveIn + amountIn);
+reserves[pair].reserve1 = uint112(reserveOut - amountOut);
+```
+- **What:** Updates stored reserves to reflect post-swap balances
+- **Why here:** After transfers complete; brings storage in sync with actual balances
+- **Assumption:** No other operations have modified pool balances since reserves were read
+- **Invariant maintained:** `reserve0 * reserve1 >= k_before * 1.003` (constant product + fee)
+- **Casting risk:** `uint112` casting could truncate if reserves exceed 2^112 - 1 (≈ 5.2e33)
+  - For most tokens with 18 decimals: limit is ~5.2e15 tokens
+  - Overflow protection: require reserves fit in uint112, else revert
+- **5 Whys:**
+  - Why update reserves? → Storage must match actual balances for next swap
+  - Why after transfers? → Need to know final state before recording
+  - Why not query balances? → Gas optimization: storage update cheaper than CALL + BALANCE
+  - Why uint112? → Pack two reserves in one storage slot (256 bits = 2 * 112 + 32 for timestamp)
+  - Why this formula? → reserveIn increased by amountIn, reserveOut decreased by amountOut
+- **Invariant verification:**
+  - Before: `k_before = reserveIn * reserveOut`
+  - After: `k_after = (reserveIn + amountIn) * (reserveOut - amountOut)`
+  - With 0.3% fee: `k_after ≈ k_before * 1.003` (fee adds permanent liquidity)
+
+---
+
+```solidity
+// L130: Event emission
+emit Swap(msg.sender, tokenIn, tokenOut, amountIn, amountOut, block.timestamp);
+```
+- **What:** Emits event logging swap details for off-chain indexing
+- **Why here:** After all state changes finalized; last operation before return
+- **Assumption:** Event watchers (subgraphs, dex aggregators) rely on this for tracking trades
+- **Data included:**
+  - `msg.sender`: Who initiated swap (for user trade history)
+  - `tokenIn/tokenOut`: Which pair was traded
+  - `amountIn/amountOut`: Exact amounts for price tracking
+  - `block.timestamp`: When trade occurred (for TWAP calculations, analytics)
+- **First Principles:** Events are write-only log for off-chain systems; don't affect on-chain state
+- **5 Hows:**
+  - How to notify off-chain? → Emit event (logs are cheaper than storage)
+  - How to structure event? → Include all relevant swap parameters
+  - How do indexers use this? → Build trade history, calculate volume, track prices
+  - How to ensure consistency? → Emit after state finalized (can't be front-run)
+  - How to query later? → Blockchain logs filtered by event signature + contract address
+
+---
+
+**Cross-Function Dependencies:**
+
+*Internal Calls:*
+- `getReserves(pair, tokenIn, tokenOut)`: Helper to read and order reserves based on token addresses
+  - Depends on: `reserves[pair]` storage being synchronized
+  - Returns: (reserveIn, reserveOut) in correct order for tokenIn/tokenOut
+
+*External Calls (Outbound):*
+- `IERC20(tokenIn).transferFrom(msg.sender, pair, amountIn)`: ERC20 standard call
+  - Assumes: tokenIn implements ERC20, user has approved Router
+  - Reentrancy risk: If tokenIn is malicious, could callback
+  - Failure: Reverts entire transaction
+- `IERC20(tokenOut).transfer(msg.sender, amountOut)`: ERC20 standard call
+  - Assumes: Pool has sufficient tokenOut balance
+  - Reentrancy risk: If tokenOut has hooks
+  - Failure: Reverts entire transaction
+
+*Called By:*
+- Users directly (external call)
+- Aggregators/routers (external call)
+- Multi-hop swap functions (internal call from same contract)
+
+*Shares State With:*
+- `addLiquidity()`: Modifies same reserves[pair], must maintain k invariant
+- `removeLiquidity()`: Modifies same reserves[pair]
+- `sync()`: Emergency function to force reserves sync with balances
+- `skim()`: Removes excess tokens beyond reserves
+
+*Invariant Coupling:*
+- **Global invariant:** `sum(all reserves[pair].reserve0 for all pairs) <= sum(all token balances in pools)`
+- **Per-pool invariant:** `reserves[pair].reserve0 * reserves[pair].reserve1 >= k_initial * (1.003^n)` where n = number of swaps
+  - Each swap increases k by 0.3% due to fee
+- **Reentrancy protection:** `nonReentrant` modifier ensures no cross-function reentrancy
+  - swap() cannot be re-entered while executing
+  - addLiquidity/removeLiquidity also cannot execute during swap
+
+*Assumptions Propagated to Callers:*
+- Caller must have approved Router to spend amountIn of tokenIn
+- Caller must set reasonable deadline (e.g., block.timestamp + 300 seconds)
+- Caller must calculate minAmountOut based on acceptable slippage (e.g., expectedOutput * 0.99 for 1%)
+- Caller assumes pair exists (or will handle "Pool does not exist" revert)

audit-context-building/resources/OUTPUT_REQUIREMENTS.md

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+# Output Requirements
+
+When performing ultra-granular analysis, Claude MUST structure output following the Per-Function Microstructure Checklist format demonstrated in [FUNCTION_MICRO_ANALYSIS_EXAMPLE.md](FUNCTION_MICRO_ANALYSIS_EXAMPLE.md).
+
+---
+
+## Required Structure
+
+For EACH analyzed function, output MUST include:
+
+**1. Purpose** (mandatory)
+- Clear statement of function's role in the system
+- Impact on system state, security, or economics
+- Minimum 2-3 sentences
+
+**2. Inputs & Assumptions** (mandatory)
+- All parameters (explicit and implicit)
+- All preconditions
+- All trust assumptions
+- Each input must identify: type, source, trust level
+- Minimum 3 assumptions documented
+
+**3. Outputs & Effects** (mandatory)
+- Return values (or "void" if none)
+- All state writes
+- All external interactions
+- All events emitted
+- All postconditions
+- Minimum 3 effects documented
+
+**4. Block-by-Block Analysis** (mandatory)
+For EACH logical code block, document:
+- **What:** What the block does (1 sentence)
+- **Why here:** Why this ordering/placement (1 sentence)
+- **Assumptions:** What must be true (1+ items)
+- **Depends on:** What prior state/logic this relies on
+- **First Principles / 5 Whys / 5 Hows:** Apply at least ONE per block
+
+Minimum standards:
+- Analyze at minimum: ALL conditional branches, ALL external calls, ALL state modifications
+- For complex blocks (>5 lines): Apply First Principles AND 5 Whys or 5 Hows
+- For simple blocks (<5 lines): Minimum What + Why here + 1 Assumption
+
+**5. Cross-Function Dependencies** (mandatory)
+- Internal calls made (list all)
+- External calls made (list all with risk analysis)
+- Functions that call this function
+- Shared state with other functions
+- Invariant couplings (how this function's invariants interact with others)
+- Minimum 3 dependency relationships documented
+
+---
+
+## Quality Thresholds
+
+A complete micro-analysis MUST identify:
+- Minimum 3 invariants (per function)
+- Minimum 5 assumptions (across all sections)
+- Minimum 3 risk considerations (especially for external interactions)
+- At least 1 application of First Principles
+- At least 3 applications of 5 Whys or 5 Hows (combined)
+
+---
+
+## Format Consistency
+
+- Use markdown headers: `**Section Name:**` for major sections
+- Use bullet points (`-`) for lists
+- Use code blocks (` ```solidity `) for code snippets
+- Reference line numbers: `L45`, `lines 98-102`
+- Separate blocks with `---` horizontal rules for readability